Take the audio tracks in a data track into account.

Depends on commit 6ec04e6 of `python-musicbrainzngs'.

beets/autotag/mb.py

@@ -217,6 +217,10 @@ def album_info(release):
         format = medium.get('format')
 
         all_tracks = medium['track-list']
+        if 'data-track-list' in medium:
+            all_tracks += medium['data-track-list']
+        total = len(all_tracks)
+
         if 'pregap' in medium:
             all_tracks.insert(0, medium['pregap'])
 
@@ -228,7 +232,7 @@ def album_info(release):
                 index,
                 int(medium['position']),
                 int(track['position']),
-                len(medium['track-list']),
+                total,
             )
             ti.disctitle = disctitle
             ti.media = format