JPEG: return YCbCrK raw data for YCbCrK JPEG in GDAL_JPEG_TO_RGB = NO mode (instead of CMYK as before) (patch from cleo, #5097)

git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@26479 f0d54148-0727-0410-94bb-9a71ac55c965