Fix for history logging label of synced subtitles based on unknown language audio track.

bazarr/subsyncer.py

@@ -60,7 +60,8 @@ class SubSyncer:
                         self.reference_stream = "s:{}".format(i)
                         break
             if not self.reference_stream:
-                using_what = "{0} embedded subtitle track".format(language_from_alpha3(embedded_subs['language'].alpha3))
+                using_what = "{0} embedded subtitle track".format(
+                    language_from_alpha3(embedded_subs['language'].alpha3) or 'unknown language audio track')
                 self.reference_stream = "s:0"
         elif 'audio' in data:
             audio_tracks = data['audio']