obs-outputs: Do not create MP4 track chunks without samples

plugins/obs-outputs/mp4-mux.c

@@ -2409,7 +2409,7 @@ static void write_packets(struct mp4_mux *mux, struct mp4_track *track)
 	struct serializer *s = mux->serializer;
 
 	size_t count = track->packets.size / sizeof(struct encoder_packet);
-	if (!count)
+	if (!count || !track->fragment_samples.num)
 		return;
 
 	struct chunk *chk = da_push_back_new(track->chunks);