Use ast_strlen_zero to see if our_contact is set or not on the dialog. It is possible for it to be a pointer to NULL.

(closes issue #11557)
Reported by: FuriousGeorge


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@94905 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -5837,7 +5837,7 @@ static int respprep(struct sip_request *resp, struct sip_pvt *p, const char *msg
 			snprintf(contact, sizeof(contact), "%s;expires=%d", p->our_contact, p->expiry);
 			add_header(resp, "Contact", contact);	/* Not when we unregister */
 		}
-	} else if (msg[0] != '4' && p->our_contact[0]) {
+	} else if (msg[0] != '4' && !ast_strlen_zero(p->our_contact)) {
 		add_header(resp, "Contact", p->our_contact);
 	}
 	return 0;