Reduce number of queries for some playlists operations.

Also allow admins to update/delete playlists from other users in the Subsonic API. Closes #1366

core/archiver.go

@@ -54,7 +54,7 @@ func (a *archiver) ZipArtist(ctx context.Context, id string, out io.Writer) erro
 }
 
 func (a *archiver) ZipPlaylist(ctx context.Context, id string, out io.Writer) error {
-	pls, err := a.ds.Playlist(ctx).Get(id)
+	pls, err := a.ds.Playlist(ctx).GetWithTracks(id)
 	if err != nil {
 		log.Error(ctx, "Error loading mediafiles from playlist", "id", id, err)
 		return err