cerbero: Always require a filename to verify()
cerbero: Always require a filename to verify()

This is simpler to understand and harder to mess up with.

GStreamer/cerbero,GStreamer/cerbero,GStreamer/cerbero,nirbheek/cerbero,nirbheek/cerbero,nirbheek/cerbero,GStreamer/cerbero,GStreamer/cerbero,nirbheek/cerbero