Exception thrown if library empty

[jrha]

If the library is empty, ssp will crash with something along the lines of:

Traceback (most recent call last):
  File "./player.py", line 239, in <module>
    p.play()
  File "./player.py", line 156, in play
    self.album = self.track.albumid # Set this so we can continue with an album we stumble across
AttributeError: 'NoneType' object has no attribute 'albumid'

Instead of this unhelpfulness, the user should be prompted to run ./update_library.py even though the README does state that it should be run before the player.