message: photo: add assertion on empty image in denoising
diff: @@ -116,6 +116,7 @@ void cv::fastNlMeansDenoising( InputArray _src, OutputArray _dst, const std::vec
  CV_INSTRUMENT_REGION()
  int hn = (int)h.size(), type = _src.type(), depth = CV_MAT_DEPTH(type), cn = CV_MAT_CN(type);
  + CV_Assert(!_src.empty());
  CV_Assert(hn == 1 || hn == cn);
  Size src_size = _src.size();
  