message: Handle DeadlineExceeded in OptimizeDatasetOp::MakeDataset correctly. Before this change, if we encounter a DeadlineExceeded error, the output dataset will not be set (i.e. be a nullptr), resulting in "Read uninitialized Dataset variant" when we try to use it.
diff: @@ -60,6 +60,10 @@ void OptimizeDatasetOp::MakeDataset(OpKernelContext* ctx, DatasetBase* input,
  if (errors::IsDeadlineExceeded(s)) {
  // Ignore DeadlineExceeded as it implies that the attempted rewrite took too
  // long which should not prevent further computation.
  + LOG(WARNING) << s.ToString();
  +
  + *output = input;
  + input->Ref();
  return;
  }
  OP_REQUIRES_OK(ctx, s);
  