Only call WebPDequantizeLevels() on cropped area
Only call WebPDequantizeLevels() on cropped area

this might change some crc slightly, since WebPDequantizeLevels()
performs an analysis pass, counting levels, which impacts the smoothing.
Now, the cropping area is not the same, so minor diffs are expected here
and there.

Change-Id: I3cce1e40c6f11c25b7c841044d637685c5740352

PKRoma/libwebp,webmproject/libwebp,webmproject/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp