TT#14008 fix logic test for SSRC substitution

Change-Id: Ib2d05229caf0bb6cba5ca38f3dcb53b55cb00d46

kernel-module/xt_RTPENGINE.c

@@ -4654,7 +4654,7 @@ no_intercept:
 
 		if (rtp2.ok) {
 			// SSRC substitution
-			if (g->target.transcoding && o->output.ssrc_out && ssrc_idx != -1)
+			if (g->target.transcoding && ssrc_idx != -1 && o->output.ssrc_out[ssrc_idx])
 				rtp2.header->ssrc = o->output.ssrc_out[ssrc_idx];
 
 			pkt_idx = packet_index(&o->encrypt, &o->output.encrypt, rtp2.header, ssrc_idx);