playlist: Keep lock when modifying PlaylistUnseenTracks.{_num_tracks,_sp_tracks_len}
playlist: Keep lock when modifying PlaylistUnseenTracks.{_num_tracks,_sp_tracks_len}

mopidy/pyspotify,kotamat/pyspotify,felix1m/pyspotify,felix1m/pyspotify,jodal/pyspotify,kotamat/pyspotify,felix1m/pyspotify,jodal/pyspotify,mopidy/pyspotify,jodal/pyspotify,kotamat/pyspotify