message: Set build_called_once to true after we call build mode
diff: @@ -1116,6 +1116,8 @@ class TrtGraphConverterV2(object):
  for inp in input_fn():
  self._converted_func(*map(ops.convert_to_tensor, inp))
  + self._build_called_once = True
  +
  def save(self, output_saved_model_dir):
  """Save the converted SavedModel.
  