message: Fix expensive decompression in JPEG GetImageInfo
  The current implementation of GetImageInfo starts a libjpeg
  decompression pass over input images. Certain images
  (e.g., progressive JPEG) trigger a full image decompression, resulting
  in a performance degradation. This commit switches to an equivalent but
  cheaper libjpeg call for evaluating image dimensions.
diff: @@ -577,7 +577,7 @@ bool GetImageInfo(const void* srcdata, int datasize, int* width, int* height,
  SetSrc(&cinfo, srcdata, datasize, false);
  jpeg_read_header(&cinfo, TRUE);
  - jpeg_start_decompress(&cinfo); // required to transfer image size to cinfo
  + jpeg_calc_output_dimensions(&cinfo);
  if (width) *width = cinfo.output_width;
  if (height) *height = cinfo.output_height;
  if (components) *components = cinfo.output_components;
  