Initialize variable.

test/core/surface/server_test.c

@@ -139,7 +139,7 @@ void test_bind_server_to_addr(const char *host, bool secure) {
 }
 
 static 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) {