Do not reject SDP packets describing only non audio streams.

(closes issue #16387)
Reported by: zalex1953
Patches:
      media-level-c-fix1.diff uploaded by mnicholson (license 96)
Tested by: mnicholson, zalex1953


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@233394 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -8703,7 +8703,7 @@ static int process_sdp(struct sip_pvt *p, struct sip_request *req, int t38action
 
 
 	/* Sanity checks */
-	if (!hp) {
+	if (!hp && !vhp && !thp && !ihp) {
 		ast_log(LOG_WARNING, "Insufficient information in SDP (c=)...\n");
 		return -1;
 	}