Fix for MPTS streams.

Without this if the input is MPTS, tsdecrypt incorrectly tries to
decrypt (and brokes) services that do not belong to the chosen
input services. An additional extra is that with this decrypting
a service in MPTS is a lot quicker since lots of unneeded work is
avoided.

process.c

 	for (i = 0; i < batch_sz; i++) {
 		uint8_t *ts_packet = data + (i * 188);
 
-		int scramble_idx = ts_packet_get_scrambled(ts_packet);
-		if (scramble_idx > 1) {
+		uint16_t pid = ts_packet_get_pid(ts_packet);
+		if (pidmap_get(&ts->pidmap, pid) && ts_packet_is_scrambled(ts_packet)) {
 			if (ts->key.is_valid_cw) {
+				int scramble_idx = ts_packet_get_scrambled(ts_packet);
 				uint8_t payload_ofs = ts_packet_get_payload_offset(ts_packet);
 				if (scramble_idx == 2) { // scramble_idx 2 == even key
 					even_pcks[even_packets].data = ts_packet + payload_ofs;
 				}
 			}
 		} else {
-			decode_packet(ts, ts_packet);
+			int allowed_pid = pidmap_get(&ts->pidmap, pid);
+			if (allowed_pid) // PAT or allowed PIDs
+				decode_packet(ts, ts_packet);
 			if (ts->pid_filter) {
-				if (pidmap_get(&ts->pidmap, pid)) // PAT or allowed PIDs
+				if (allowed_pid) // PAT or allowed PIDs
 					output_write(ts, ts_packet, 188);
 			} else {
 				output_write(ts, ts_packet, 188);