modules_k/uac: fix from/to restore for small original URI

Seems that the URI length check is superfluous and fails under
certain conditions. It does not make sense for the URI to have
zero bytes, so just use the first seen zero byte as end marker.

I have a reproducible test case where the restore inserts URI
with multiple zero-bytes to wire. This happens if the original
URI is smaller than the one we rewrote it to using uac_replace_from.

modules_k/uac/from.c

@@ -463,15 +463,17 @@ int restore_from( struct sip_msg *msg, int *is_from )
 		LM_ERR("new URI shorter than old URI\n");
 		goto failed;
 	}
-	for( i=0 ; i<old_uri.len ; i++ )
+	for( i=0 ; i<old_uri.len ; i++ ) {
 		new_uri.s[i] ^= old_uri.s[i];
-	if (new_uri.len==old_uri.len) {
-		for( ; new_uri.len && (new_uri.s[new_uri.len-1]==0) ; new_uri.len-- );
-		if (new_uri.len==0) {
-			LM_ERR("new URI got 0 len\n");
-			goto failed;
+		if (new_uri.s[i] == 0) {
+			new_uri.len = i;
+			break;
 		}
 	}
+	if (new_uri.len==0) {
+		LM_ERR("new URI got 0 len\n");
+		goto failed;
+	}
 
 	LM_DBG("decoded uris are: new=[%.*s] old=[%.*s]\n",
 		new_uri.len, new_uri.s, old_uri.len, old_uri.s);