advance_to_track: ignore same-index calls so requesting the current track no longer restarts it

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/DynamicSoundPlayerCore.gd

@@ -144,6 +144,8 @@ func advance_to_track(index: int) -> void:
 	var playlist : DynamicSoundPlaylist = _player.Playlist;
 	if playlist == null or index < 0 or index >= playlist.QueuedSongs.size():
 		return;
+	if index == _current_index and not _active_songs.is_empty():
+		return;
 	if _playback == null:
 		_player.play();
 		_playback = _player.get_stream_playback();