mythmusic: Fix saving active playlist to an existing playlist

(cherry picked from commit 3468a38)

Signed-off-by: Stuart Morgan <smorgan@mythtv.org>

mythplugins/mythmusic/mythmusic/musiccommon.cpp

@@ -1471,6 +1471,7 @@ void MusicCommon::customEvent(QEvent *event)
             QString songList = gPlayer->getPlaylist()->toRawSonglist();
             playlist->removeAllTracks();
             playlist->fillSongsFromSonglist(songList);
+            playlist->changed();
             gPlayer->playlistChanged(playlist->getID());
         }
     }