chan_rtp.c: Fix uninitialized memory crash.

unicast_rtp_request() could pass an uninitialized 'us' parameter to
ast_ouraddrfor().  If ast_ouraddrfor() returns an error then the 'us'
parameter may not get initialized.  Thus when the code tries to save the
'us' parameter to the local address we could try to copy a ridiculous
sized memory buffer and segfault.

* Made pass an initialized 'us' parameter to ast_ouraddrfor() and abort
the UnicastRTP channel request if it fails.

ASTERISK-26672

Change-Id: I1ef7a7c09f4da4f15dcb6de660d2bcac5f2a95c0

channels/chan_rtp.c

@@ -316,7 +316,12 @@ static struct ast_channel *unicast_rtp_request(const char *type, struct ast_form
 	engine_name = S_COR(ast_test_flag(&opts, OPT_RTP_ENGINE),
 		opt_args[OPT_ARG_RTP_ENGINE], "asterisk");
 
-	ast_ouraddrfor(&address, &local_address);
+	ast_sockaddr_copy(&local_address, &address);
+	if (ast_ouraddrfor(&address, &local_address)) {
+		ast_log(LOG_ERROR, "Could not get our address for sending media to '%s'\n",
+			args.destination);
+		goto failure;
+	}
 	instance = ast_rtp_instance_new(engine_name, NULL, &local_address, NULL);
 	if (!instance) {
 		ast_log(LOG_ERROR,