function stopTrack() {
	if (current_track_id !== null) {
		audioTracks[current_track_id].stop();
		current_track_id = null;
	}
}
stop the current audio track
@see {@link playTrack}
@example
// play a awesome music
me.audio.playTrack("awesome_music");
// stop the current music
me.audio.stopTrack();