Foil Presenter Importer fails if no verses

http://support.openlp.org/issues/1931

The Foil Presenter song import if the song does not contain any verses.

OpenLP Bug Report
Version: {u'full': u'2.0.1', u'version': u'2.0.1', u'build': None}

--- Details of the Exception. ---

i was importing foilpresenter documents

--- Exception Traceback ---
Traceback (most recent call last):
File "/Users/martin/Documents/openlp/2.0/build/pyi.darwin/OpenLP/out00-PYZ.pyz/openlp.core.ui.wizard", line 188, in onCurrentIdChanged
File "/Users/martin/Documents/openlp/2.0/build/pyi.darwin/OpenLP/out00-PYZ.pyz/openlp.plugins.songs.forms.songimportform", line 391, in performWizard
File "/Users/martin/Documents/openlp/2.0/build/pyi.darwin/OpenLP/out00-PYZ.pyz/openlp.plugins.songs.lib.foilpresenterimport", line 134, in doImport
File "/Users/martin/Documents/openlp/2.0/build/pyi.darwin/OpenLP/out00-PYZ.pyz/openlp.plugins.songs.lib.foilpresenterimport", line 234, in xml_to_song
File "/Users/martin/Documents/openlp/2.0/build/pyi.darwin/OpenLP/out00-PYZ.pyz/openlp.plugins.songs.lib.foilpresenterimport", line 427, in process_lyrics
File "lxml.objectify.pyx", line 226, in lxml.objectify.ObjectifiedElement._getattr__ (src/lxml/lxml.objectify.c:2894)
File "lxml.objectify.pyx", line 485, in lxml.objectify._lookupChildOrRaise (src/lxml/lxml.objectify.c:5428)
AttributeError: no such child: strophe

--- System information ---
Platform: Darwin-12.2.0-x86_64-i386-32bit

--- Library Versions ---
Python: 2.7.3
Qt4: 4.8.3
Phonon: 4.4.0
PyQt4: 4.9.4
QtWebkit: 534.34
SQLAlchemy: 0.7.9
SQLAlchemy Migrate: 0.7.2
BeautifulSoup: 3.2.1
lxml: 2.3.2
Chardet: 2.0.1
PyEnchant: -
PySQLite: -
Mako: 0.7.2
pyUNO bridge: -