#407 NegativeOrZeroImageSize exception on GIFs

[Tianyu Lang]

These GIF files can be viewed on Chrome and Firefox. They can be transcoded to mp4 with FFMPEG. And they can also be identified with Gifsicle.

I think these GIFs might have redundant data in their extension headers. The softwares listed above will ignore them but GM is affected by them. Bug in the LZW decoding code can also be a reason.

[Tianyu Lang]

Here is the zipped version since sourceforge can potentially sanitize the images uploaded.