Game Over page throws an error when the .pacmacs-score file is empty

[rexim]

Steps to reproduce:

• Edit .pacmacs-score file so it doesn't contain s-expressions. The easiest case is just an empty file.
• Start the game
• Die to reach the Game Over page

Observer: an error in the *Message* buffer: Error running timer pacmacs-tick': (end-of-file)
Expected: something less scary. Ideally we should treat incorrect .pacmacs-score as a table that doesn't contain any records.