Coverflow can crash unity

When results are added to and removed from the coverflow renderer rapidly, it can crash, because it doesn't seem to be disconnecting the IconLoader handles.

Backtrace of the crash:

Program received signal SIGSEGV, Segmentation fault.
0x00007fffe1dbb116 in unity::dash::CoverflowResultItem::CoverflowResultItem(unity::dash::Result&, unity::dash::CoverflowResultView*, nux::ObjectPtr<nux::CoverflowModel>)::{lambda(nux::BaseTexture*)#1}::operator()(nux::BaseTexture*) const () at ~/unity/source/unity/dash/CoverflowResultView.cpp:93
93 parent_->NeedRedraw();
#0 0x00007fffe1dbb116 in unity::dash::CoverflowResultItem::CoverflowResultItem(unity::dash::Result&, unity::dash::CoverflowResultView*, nux::ObjectPtr<nux::CoverflowModel>)::{lambda(nux::BaseTexture*)#1}::operator()(nux::BaseTexture*) const () at ~/unity/source/unity/dash/CoverflowResultView.cpp:93
No symbol table info available.
#1 0x00007fffe1dbd110 in sigc::adaptor_functor<unity::dash::CoverflowResultItem::CoverflowResultItem(unity::dash::Result&, unity::dash::CoverflowResultView*, nux::CoverflowModel::Ptr)::<lambda(nux::BaseTexture*)> >::operator()<nux::BaseTexture* const&>(nux::BaseTexture * const&) const (this=0x58e84f0, _A_arg1=@0x7fffffffd5e0: 0x61ab5f0) at /usr/include/sigc++-2.0/sigc++/adaptors/adaptor_trait.h:84
No locals.
#2 0x00007fffe1dbcfdf in sigc::internal::slot_call1<unity::dash::CoverflowResultItem::CoverflowResultItem(unity::dash::Result&, unity::dash::CoverflowResultView*, nux::CoverflowModel::Ptr)::<lambda(nux::BaseTexture*)>, void, nux::BaseTexture*>::call_it(sigc::internal::slot_rep *, sigc::type_trait<nux::BaseTexture*>::take) (rep=0x58e84c0, a_1=@0x7fffffffd5e0: 0x61ab5f0) at /usr/include/sigc++-2.0/sigc++/functors/slot.h:137
        typed_rep = 0x58e84c0
#3 0x00007fffe1e93e6c in sigc::internal::signal_emit1<void, nux::BaseTexture*, sigc::nil>::emit (impl=0x5f171b0, _A_a1=@0x7fffffffd5e0: 0x61ab5f0) at /usr/include/sigc++-2.0/sigc++/signal.h:1010
        it = {_M_node = 0x5f167f0}
        exec = {sig_ = 0x5f171b0}
        slots = {slots_ = @0x5f171b8, placeholder = {_M_node = 0x5932890}}
#4 0x00007fffe1e939e9 in sigc::signal1<void, nux::BaseTexture*, sigc::nil>::emit (this=0x5f16fc8, _A_a1=@0x7fffffffd5e0: 0x61ab5f0) at /usr/include/sigc++-2.0/sigc++/signal.h:2781
No locals.
#5 0x00007fffe1e92d75 in unity::IconTexture::IconLoaded (this=0x5f16ba0, icon_name=..., size=132, pixbuf=...) at ~/unity/source/unity/unity-shared/IconTexture.cpp:176
No locals.
#6 0x00007fffe1e94015 in sigc::bound_mem_functor3<void, unity::IconTexture, std::string const&, unsigned int, unity::glib::Object<_GdkPixbuf> const&>::operator() (this=0x59dc060, _A_a1=..., _A_a2=@0x7fffffffd65c: 132, _A_a3=...) at /usr/include/sigc++-2.0/sigc++/functors/mem_fun.h:1985
No locals.
#7 0x00007fffe1e93ac6 in std::_Function_handler<void (std::string const&, unsigned int, unity::glib::Object<_GdkPixbuf> const&), sigc::bound_mem_functor3<void, unity::IconTexture, std::string const&, unsigned int, unity::glib::Object<_GdkPixbuf> const&> >::_M_invoke(std::_Any_data const&, std::string const&, unsigned int, unity::glib::Object<_GdkPixbuf> const&) (__functor=..., __args#0=..., __args#1=132, __args#2=...) at /usr/include/c++/4.6/functional:1778
No locals.
#8 0x00007fffe1e7d24a in std::function<void (std::string const&, unsigned int, unity::glib::Object<_GdkPixbuf> const&)>::operator()(std::string const&, unsigned int, unity::glib::Object<_GdkPixbuf> const&) const (this=0x59dbfc0, __args#0=..., __args#1=132, __args#2=...) at /usr/include/c++/4.6/functional:2161
No locals.
#9 0x00007fffe1e7a8f8 in unity::IconLoader::Impl::IconLoaderTask::InvokeSlot (this=0x59dbfa0) at ~/unity/source/unity/unity-shared/IconLoader.cpp:129
No locals.
#10 0x00007fffe1e799e1 in unity::IconLoader::Impl::CoalesceTasksCb (this=0x1d79580) at ~/unity/source/unity/unity-shared/IconLoader.cpp:785
        task = 0x59dbfa0
        __for_range = @0x1d79660: {<std::_Vector_base<unity::IconLoader::Impl::IconLoaderTask*, std::allocator<unity::IconLoader::Impl::IconLoaderTask*> >> = {_M_impl = {<std::allocator<unity::IconLoader::Impl::IconLoaderTask*>> = {<__gnu_cxx::new_allocator<unity::IconLoader::Impl::IconLoaderTask*>> = {<No data fields>}, <No data fields>}, _M_start = 0x1d94c50, _M_finish = 0x1d94c78, _M_end_of_storage = 0x1d94e50}}, <No data fields>}
        __for_begin = {_M_current = 0x1d94c58}
        __for_end = {_M_current = 0x1d94c78}
#11 0x00007fffe1e81463 in sigc::bound_mem_functor0<bool, unity::IconLoader::Impl>::operator() (this=0x59f03a0) at /usr/include/sigc++-2.0/sigc++/functors/mem_fun.h:1787
No locals.
#12 0x00007fffe1e7f2ca in std::_Function_handler<bool (), sigc::bound_mem_functor0<bool, unity::IconLoader::Impl> >::_M_invoke(std::_Any_data const&) (__functor=...) at /usr/include/c++/4.6/functional:1764
No locals.
#13 0x00007fffe02e1c4a in std::function<bool ()>::operator()() const (this=0x5d80410) at /usr/include/c++/4.6/functional:2161
No locals.
#14 0x00007fffe02e01c0 in unity::glib::Source::SourceCallback (data=0x611b750) at ~/unity/source/unity/UnityCore/GLibSource.cpp:106
        self = 0x5d803e0
#15 0x00007ffff5a3f91b in g_timeout_dispatch (source=0x5a2fb40, callback=<optimized out>, user_data=<optimized out>) at /build/buildd/glib2.0-2.32.3/./glib/gmain.c:3882
        timeout_source = 0x5a2fb40
        again = <optimized out>
#16 0x00007ffff5a3ed53 in g_main_dispatch (context=0x62de00) at /build/buildd/glib2.0-2.32.3/./glib/gmain.c:2539
        dispatch = 0x7ffff5a3f900 <g_timeout_dispatch>
        was_in_call = 0
        user_data = 0x611b750
        callback = 0x7fffe02e0170 <unity::glib::Source::SourceCallback(void*)>
        cb_funcs = 0x7ffff5cea9a0
        cb_data = 0x5aff880
        current_source_link = {data = 0x5a2fb40, next = 0x0}
        need_destroy = <optimized out>
        source = 0x5a2fb40
        current = 0x8cd720
        i = <optimized out>
#17 g_main_context_dispatch (context=0x62de00) at /build/buildd/glib2.0-2.32.3/./glib/gmain.c:3075
No locals.
#18 0x00007ffff5a3f0a0 in g_main_context_iterate (dispatch=1, block=<optimized out>, context=0x62de00, self=<optimized out>) at /build/buildd/glib2.0-2.32.3/./glib/gmain.c:3146
        timeout = 0
        some_ready = 1
        fds = <optimized out>
        max_priority = 240
        nfds = 15
        allocated_nfds = <optimized out>
#19 g_main_context_iterate (context=0x62de00, block=<optimized out>, dispatch=1, self=<optimized out>) at /build/buildd/glib2.0-2.32.3/./glib/gmain.c:3083
        some_ready = 1
#20 0x00007ffff5a3f49a in g_main_loop_run (loop=0x62e260) at /build/buildd/glib2.0-2.32.3/./glib/gmain.c:3340
        __PRETTY_FUNCTION__ = "g_main_loop_run"
#21 0x00007ffff7ac9418 in compiz::private_screen::EventManager::startEventLoop (this=0x62bfb0, dpy=0x630a40) at ~/unity/source/compiz/src/screen.cpp:172
No locals.
#22 0x00007ffff7ac939b in CompScreenImpl::eventLoop (this=0x627bc0) at ~/unity/source/compiz/src/screen.cpp:159
No locals.
#23 0x0000000000416657 in CompManager::run (this=0x7fffffffd9c0) at ~/unity/source/compiz/src/main.cpp:191
No locals.
#24 0x00000000004168c8 in main (argc=3, argv=0x7fffffffdac8) at ~/unity/source/compiz/src/main.cpp:260
        manager = {disableSm = false, clientId = 0x0, displayName = 0x0}