message: fix bug in keras when only pass run options will trigger segmentation fault
diff: @@ -235,18 +235,13 @@ void RunCallableHelper(tensorflow::Session* session, int64_t handle,
  }
  }
  - // Allocate a RunMetadata protobuf object to receive the metadata,
  - // if the caller is expecting any.
  - std::unique_ptr<RunMetadata> run_metadata_proto;
  - if (run_metadata != nullptr) {
  - run_metadata_proto.reset(new RunMetadata);
  - }
  + RunMetadata run_metadata_proto;
  // Run the callable.
  std::vector<Tensor> output_tensors;
  Py_BEGIN_ALLOW_THREADS;
  s = session->RunCallable(handle, input_tensors, &output_tensors,
  - run_metadata_proto.get());
  + &run_metadata_proto);
  Py_END_ALLOW_THREADS;
  if (!s.ok()) {
  @@ -256,7 +251,7 @@ void RunCallableHelper(tensorflow::Session* session, int64_t handle,
  // If requested, serialize the RunMetadata to pass it back to the caller.
  if (run_metadata != nullptr) {
  - s = MessageToBuffer(*run_metadata_proto, run_metadata);
  + s = MessageToBuffer(run_metadata_proto, run_metadata);
  if (!s.ok()) {
  Set_TF_Status_from_Status(out_status, s);
  return;
  