Beautifier: Prevent writing of an empty documentation file

Only keep successfully created documentation files. Thus the automatic
generation of a file can be triggered again.

Change-Id: I8ec3becfd2f3387f18635741dd11288cb72c372d
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: David Schulz <david.schulz@digia.com>