message: fixing bug for when num of trees is not set
diff: @@ -126,14 +126,15 @@ def model_builder(features,
  create_estimator_spec_op = getattr(head, "create_estimator_spec", None)
  + training_hooks = []
  if num_trees:
  if center_bias:
  num_trees += 1
  +
  finalized_trees, attempted_trees = gbdt_model.get_number_of_trees_tensor()
  - training_hooks = [
  + training_hooks.append(
  trainer_hooks.StopAfterNTrees(num_trees, attempted_trees,
  - finalized_trees)
  - ]
  + finalized_trees))
  if output_type == ModelBuilderOutputType.MODEL_FN_OPS:
  if use_core_libs and callable(create_estimator_spec_op):
  