message: Avoid getting min/max information when min/max are empty.
diff: @@ -46,12 +46,16 @@ TfLiteStatus CalibrationReader::AddCalibrationToModel(ModelT* model,
  if (update) {
  auto tensor = subgraph->tensors[tensorid_stat.first].get();
  if (tensor->quantization) {
  + if (!tensor->quantization->min.empty()) {
  const float existing_min = tensor->quantization->min[0];
  - const float existing_max = tensor->quantization->max[0];
  min = min < existing_min ? min : existing_min;
  + }
  + if (!tensor->quantization->max.empty()) {
  + const float existing_max = tensor->quantization->max[0];
  max = max > existing_max ? max : existing_max;
  }
  }
  + }
  auto quant_params = absl::make_unique<tflite::QuantizationParametersT>();
  quant_params->min.push_back(min);
  quant_params->max.push_back(max);
  