res_rtp_asterisk.c: Initialize ourip passed to ast_find_ourip().

We access uninitialized memory when the 'ourip' parameter does not
have an initial guess to our IP address.

ASTERISK-26672

Change-Id: I35507ea1ad7455d2be188f6ccdd4add7bd150e15

res/res_rtp_asterisk.c

@@ -4912,9 +4912,11 @@ static void ast_rtp_prop_set(struct ast_rtp_instance *instance, enum ast_rtp_pro
 			ast_sockaddr_set_port(&rtp->rtcp->us,
 					      ast_sockaddr_port(&rtp->rtcp->us) + 1);
 
+			ast_sockaddr_copy(&local_addr, &rtp->rtcp->us);
 			if (!ast_find_ourip(&local_addr, &rtp->rtcp->us, 0)) {
 				ast_sockaddr_set_port(&local_addr, ast_sockaddr_port(&rtp->rtcp->us));
 			} else {
+				/* Failed to get local address reset to use default. */
 				ast_sockaddr_copy(&local_addr, &rtp->rtcp->us);
 			}