init another one

test/core/end2end/dualstack_socket_test.c

@@ -273,7 +273,7 @@ void test_connect(const char *server_host, const char *client_host, int port,
 }
 
 int external_dns_works(const char *host) {
-  grpc_resolved_addresses *res;
+  grpc_resolved_addresses *res = NULL;
   grpc_error *error = grpc_blocking_resolve_address(host, "80", &res);
   GRPC_ERROR_UNREF(error);
   if (res != NULL) {