sip/request: fix msg->scode null pointer dereference (found by Clang Static Analyzer)
@@ -145,7 +145,7 @@ static void response_handler(int err, const struct sip_msg *msg, void *arg)
req->ct = NULL;
- if (!req->canceled && (err || msg->scode == 503) &&
+ if (!req->canceled && (err || (msg && msg->scode == 503)) &&
(req->addrl.head || req->srvl.head)) {
err = request_next(req);
