Comment 0 for bug 1534306

Empty song-titles causes tracebacks on update from 2.0 to 2.2.

This basically prevents users from using songs OpenLP 2.2 after upgrading.

The traceback:

Traceback (most recent call last):
File "C:\Program Files (x86)\OpenLP\plugins\songs\songsplugin.py", line 206, in on_song_import_item_clicked
self.media_item.on_import_click()
File "D:\OpenLP_Development\OpenLP_Code\2.2\openlp\plugins\songs\lib\mediaitem.py", line 298, in on_import_click
File "D:\OpenLP_Development\OpenLP_Code\2.2\openlp\core\common\registry.py", line 137, in execute
File "D:\OpenLP_Development\OpenLP_Code\2.2\openlp\plugins\songs\lib\mediaitem.py", line 219, in on_song_list_load
File "D:\OpenLP_Development\OpenLP_Code\2.2\openlp\plugins\songs\lib\mediaitem.py", line 165, in on_search_text_button_clicked
File "D:\OpenLP_Development\OpenLP_Code\2.2\openlp\plugins\songs\lib\mediaitem.py", line 206, in search_entire
File "D:\OpenLP_Development\OpenLP_Code\2.2\openlp\core\lib\db.py", line 372, in get_all_objects
File "c:\Python33\lib\site-packages\sqlalchemy\orm\query.py", line 2292, in all
File "c:\Python33\lib\site-packages\sqlalchemy\orm\loading.py", line 72, in instances
File "c:\Python33\lib\site-packages\sqlalchemy\orm\loading.py", line 72, in <listcomp>
File "c:\Python33\lib\site-packages\sqlalchemy\orm\loading.py", line 455, in _instance
File "c:\Python33\lib\site-packages\sqlalchemy\event\attr.py", line 257, in __call__
File "c:\Python33\lib\site-packages\sqlalchemy\orm\mapper.py", line 2650, in _event_on_load
File "D:\OpenLP_Development\OpenLP_Code\2.2\openlp\plugins\songs\lib\db.py", line 134, in init_on_load
File "D:\OpenLP_Development\OpenLP_Code\2.2\openlp\core\utils\__init__.py", line 532, in get_natural_key
IndexError: string index out of range