res_pjsip_sdp_rtp: Don't produce an invalid media stream with no formats.

Depending on configuration it was possible for a media stream to be
created without any media formats. The produced SDP would fail internal
validation and cause a crash.

The code will now no longer add media streams with no formats to the SDP,
allowing it to pass validation and work.

(closes issue ASTERISK-22858)
Reported by: Anthony Messina
........

Merged revisions 403223 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@403224 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_pjsip_sdp_rtp.c

@@ -983,6 +983,11 @@ static int create_outgoing_sdp_stream(struct ast_sip_session *session, struct as
 		}
 	}
 
+	/* If no formats were actually added to the media stream don't add it to the SDP */
+	if (!media->desc.fmt_count) {
+		return 1;
+	}
+
 	/* If ptime is set add it as an attribute */
 	if (min_packet_size) {
 		snprintf(tmp, sizeof(tmp), "%d", min_packet_size);