Created by: chengduoZH

When doing detection task, the output of model may be empty. In this situation, how to check the output of model is empty or not? One solution is that:

paddle_error paddle_check_args_empty(paddle_arguments inArgs, int* notEmpty) {
  auto in = paddle::capi::cast<paddle::capi::CArguments>(inArgs);
  if (in == nullptr || notEmpty == nullptr) return kPD_NULLPTR;

  // first checking
  paddle_matrix result = paddle_matrix_create_none();
  paddle_error res_err = paddle_arguments_get_value(in, 0, result);
  if (res_err == kPD_OUT_OF_RANGE || res_err == kPD_NULLPTR) {
    *notEmpty = 0;
    CHECK(paddle_matrix_destroy(result));
    return kPD_NO_ERROR;
  }

  // second checking
  int height = 0, width = 0;
  CHECK(paddle_matrix_get_shape(result, &height, &width));
  CHECK(paddle_matrix_destroy(result));

  *notEmpty = height;
  return kPD_NO_ERROR;
}