MT#55283 check for null return first

Don't crash on undecodable packets

Fixes #2004

Change-Id: I138d7c99aaedfea12adf520d0b29ffd70ebfbe69

recording-daemon/packet.c

@@ -116,20 +116,19 @@ static void packet_decode(ssrc_t *ssrc, packet_t *packet) {
 
 		dbg("payload type for %u is %s", payload_type, payload_str);
 
-		pthread_mutex_lock(&mf->mix_lock);
+		LOCK(&mf->mix_lock);
 		ssrc->decoders[payload_type] = decoder_new(payload_str, format, ptime);
 
-		mix_sink_init(&ssrc->decoders[payload_type]->mix_sink, ssrc, &mf->mix,
-				resample_audio);
-		mix_sink_init(&ssrc->decoders[payload_type]->tls_mix_sink, ssrc, &mf->tls_mix,
-				tls_resample);
-
-		pthread_mutex_unlock(&mf->mix_lock);
 		if (!ssrc->decoders[payload_type]) {
-			ilog(LOG_WARN, "Cannot decode RTP payload type %u (%s)",
+			ilog(LOG_WARN | LOG_FLAG_LIMIT, "Cannot decode RTP payload type %u (%s)",
 					payload_type, payload_str);
 			return;
 		}
+
+		mix_sink_init(&ssrc->decoders[payload_type]->mix_sink, ssrc, &mf->mix,
+				resample_audio);
+		mix_sink_init(&ssrc->decoders[payload_type]->tls_mix_sink, ssrc, &mf->tls_mix,
+				tls_resample);
 	}
 
 	if (decoder_input(ssrc->decoders[payload_type], &packet->payload, ntohl(packet->rtp->timestamp),