chan_sip: Handle invalid SDP answer to T.38 re-invite

The chan_sip module performs a T.38 re-invite using a single media
stream of udptl, and expects the SDP answer to be the same.

If an SDP answer is received instead that contains an additional
media stream with no joint codec a crash will occur as the code
assumes that at least one joint codec will exist in this
scenario.

This change removes this assumption.

ASTERISK-28465

Change-Id: I8b02845b53344c6babe867a3f0a5231045c7ac87

channels/chan_sip.c

@@ -10965,7 +10965,13 @@ static int process_sdp(struct sip_pvt *p, struct sip_request *req, int t38action
 			    ast_rtp_lookup_mime_multiple2(s3, NULL, newnoncodeccapability, 0, 0));
 	}
 
-	if (portno != -1 || vportno != -1 || tportno != -1) {
+	/* When UDPTL is negotiated it is expected that there are no compatible codecs as audio or
+	 * video is not being transported, thus we continue in this function further up if that is
+	 * the case. If we receive an SDP answer containing both a UDPTL stream and another media
+	 * stream however we need to check again to ensure that there is at least one joint codec
+	 * instead of assuming there is one.
+	 */
+	if ((portno != -1 || vportno != -1 || tportno != -1) && ast_format_cap_count(newjointcapability)) {
 		/* We are now ready to change the sip session and RTP structures with the offered codecs, since
 		   they are acceptable */
 		unsigned int framing;