Loading Vorbis file with invalid rating value fails

Trying to load a Vorbis file with a rating: tag which contains a non-numeric string fails

E: 08:49:39,038 /home/phw/devel/musicbrainz/picard/picard/util/thread.run:56: Traceback (most recent call last):
File "/home/phw/devel/musicbrainz/picard/picard/util/thread.py", line 52, in run
result = self.func()
File "/home/phw/devel/musicbrainz/picard/picard/file.py", line 123, in _load_check
return self._load(filename)
File "/home/phw/devel/musicbrainz/picard/picard/formats/vorbis.py", line 98, in _load
value = str(int(round((float(value) * (config.setting['rating_steps'] - 1)))))
ValueError: could not convert string to float: 'TEST'