gdal_translate: don't add 0.1 when -scale is used with a dstmin equal to dstmax (usefull to generate a raster with uniform color, i.e. scaleRatio = 0)

git-svn-id: https://svn.osgeo.org/gdal/trunk@26872 f0d54148-0727-0410-94bb-9a71ac55c965