base/res/partner/partner.py: unconditional use of partner_id in name_get()

name_get() in partner.py assumes that a res.partner.address will always contain a partner_id. However the field is not set as required and the ondelete method is 'set null'. So it's quite possible for partner_id to be NULL.

I encountered this error when trying to access the Internal Moves tree in Stock Management:

File "/usr/lib/openerp-server/osv/osv.py", line 59, in wrapper
     return f(self, dbname, *args, **kwargs)
File "/usr/lib/openerp-server/osv/osv.py", line 118, in execute
     res = pool.execute_cr(cr, uid, obj, method, *args, **kw)
File "/usr/lib/openerp-server/osv/osv.py", line 110, in execute_cr
   return getattr(object, method)(cr, uid, *args, **kw)
File "/usr/lib/openerp-server/osv/orm.py", line 2077, in read
    result = self._read_flat(cr, user, select, fields, context, load)
File "/usr/lib/openerp-server/osv/orm.py", line 2188, in _read_flat
    res2 = self._columns[f].get(cr, self, ids, f, user, context=context, values=res)
File "/usr/lib/openerp-server/osv/fields.py", line 310, in get
     names = dict(obj.name_get(cr, user, filter(None, res.values()), context))
File "/usr/lib/openerp-server/addons/base/res/partner/partner.py", line 311, in name_get
     res.append((r['id'], r['partner_id'][1]))
TypeError: 'bool' object is unsubscriptable

r['partner_id'] is False at this point.