OpenLP 2 database import fails when using an old database

[Andreas Preikschat]

Hello,

1) Go to "Tools -> Re-run first time wizard"
2) Choose to download the English or German song database

Result:
A traceback is shown.

This bug has been introduced in revision 1811.

**OpenLP Bug Report**
Version: {u'full': u'1.9.7-bzr1812', u'version': u'1.9.7', u'build': u'bzr1812'}

--- Exception Traceback ---
Traceback (most recent call last):
  File "/home/andreas/Projekte/openlp/trunk/openlp/core/ui/mainwindow.py", line 783, in onFirstTimeWizardClicked
    self.firstTime()
  File "/home/andreas/Projekte/openlp/trunk/openlp/core/ui/mainwindow.py", line 755, in firstTime
    plugin.firstTime()
  File "/home/andreas/Projekte/openlp/trunk/openlp/plugins/songs/songsplugin.py", line 255, in firstTime
    importer.doImport()
  File "/home/andreas/Projekte/openlp/trunk/openlp/plugins/songs/lib/olpimport.py", line 140, in doImport
    if source_media_files_songs_table:
  File "/usr/lib/python2.7/site-packages/sqlalchemy/sql/expression.py", line 1672, in __nonzero__
    raise TypeError("Boolean value of this clause is not defined")
TypeError: Boolean value of this clause is not defined

--- System information ---
Plattform: Linux-3.1.4-1-ARCH-i686-Intel-R-_Pentium-R-_4_CPU_1.80GHz-with-glibc2.0

--- Library Versions ---
Python: 2.7.2
Qt4: 4.7.4
Phonon: 4.5.1
PyQt4: 4.8.6
SQLAlchemy: 0.7.2
SQLAlchemy Migrate: 0.7.1
BeautifulSoup: 3.2.0
lxml: 2.3.1
Chardet: 2.0.1
PyEnchant: 1.6.5
PySQLite: 1.0.1
Mako: 0.5.0
pyUNO bridge: 3.4