Skip check for extension when subscribing for MWI.

Since the remote side is not actually subscribing to a specific extension when
subscribing for MWI just skip the check to see if the extension exists. They can't use it
to specify the mailbox either since we require configuration of that in sip.conf

(closes issue #14531)
Reported by: festr


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@178205 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -15504,7 +15504,7 @@ static int handle_request_message(struct sip_pvt *p, struct sip_request *req)
 /*! \brief  Handle incoming SUBSCRIBE request */
 static int handle_request_subscribe(struct sip_pvt *p, struct sip_request *req, struct sockaddr_in *sin, int seqno, char *e)
 {
-	int gotdest;
+	int gotdest = 0;
 	int res = 0;
 	int firststate = AST_EXTENSION_REMOVED;
 	struct sip_peer *authpeer = NULL;
@@ -15612,8 +15612,10 @@ static int handle_request_subscribe(struct sip_pvt *p, struct sip_request *req,
 		return 0;
 	}
 
-	/* Get destination right away */
-	gotdest = get_destination(p, NULL);
+	if (strcmp(event, "message-summary")) {
+		/* Get destination right away */
+		gotdest = get_destination(p, NULL);
+	}
 
 	/* Get full contact header - this needs to be used as a request URI in NOTIFY's */
 	parse_ok_contact(p, req);