OpenLP crashes on startup if VLC is not installed on Linux

[Raoul Snyman]

2012-04-27 19:20:58,749 openlp.core.ui.media DEBUG get_media_players
2012-04-27 19:20:58,978 root ERROR Traceback (most recent call last):
  File "/usr/bin/openlp", line 42, in <module>
    main()
  File "/usr/lib/pymodules/python2.6/openlp/core/__init__.py", line 291, in main
    sys.exit(app.run(qt_args))
  File "/usr/lib/pymodules/python2.6/openlp/core/__init__.py", line 130, in run
    self.mainWindow = MainWindow(self.clipboard(), self.args)
  File "/usr/lib/pymodules/python2.6/openlp/core/ui/mainwindow.py", line 672, in __init__
    self.pluginManager.hook_media_manager()
  File "/usr/lib/pymodules/python2.6/openlp/core/lib/pluginmanager.py", line 131, in hook_media_manager
    plugin.createMediaManagerItem()
  File "/usr/lib/pymodules/python2.6/openlp/core/lib/plugin.py", line 224, in createMediaManagerItem
    self, self.icon)
  File "/usr/lib/pymodules/python2.6/openlp/plugins/media/lib/mediaitem.py", line 82, in __init__
    self.mediaController.previewDisplay)
  File "/usr/lib/pymodules/python2.6/openlp/core/ui/media/mediacontroller.py", line 272, in setup_display
    player.setup(display)
  File "/usr/lib/pymodules/python2.6/openlp/core/ui/media/vlcplayer.py", line 112, in setup
    display.vlcMediaPlayer = display.vlcInstance.media_player_new()
  File "/usr/lib/pymodules/python2.6/openlp/core/ui/media/vlc.py", line 894, in media_player_new
    p._instance = self
AttributeError: 'NoneType' object has no attribute '_instance'
None