add: last_chain = NULL; last_ts_chain = NULL;
context: StopTrack (){	LockMutex (soundSource[SPEECH_SOURCE].stream_mutex);	StopStream (SPEECH_SOURCE);	UnlockMutex (soundSource[SPEECH_SOURCE].stream_mutex);	if (first_chain)	{		destroy_soundchain (first_chain);		first_chain = NULL;	}	if (sound_sample)	{		DestroyMutex (track_mutex);		TFBSound_DeleteBuffers (sound_sample->num_buffers, sound_sample->buffer);		HFree (sound_sample->buffer);		HFree (sound_sample->buffer_tag);		HFree (sound_sample);		sound_sample = NULL;	}	tct = tcur = 0;	cur_page = 0;	do_subtitles ((void *)~0);}