image/gif: Encode creates corrupt GIF files from SubImages trimmed from the bottom #20692
Description
If you have an image with bounds (0,0)-(W,H), then create a SubImage with bounds (0, 0)-(W,H-n), and encode that sub image, the result is corrupt. Firefox, Chrome, and Safari will display the GIF just fine, but other more strict parsers, including image/gif's decoder, will see trailing data in the image's LZW stream and fail.
A CL to fix this is on its way...