SkGifCodec: intersect frameRect with image size

When clearing due to SkCodecAnimation::RestoreBGColor_DisposalMethod,
intersect the frameRect with the image size to prevent clearing outside
the bounds of the allocated memory.

Add a test image, created by the fuzzer.

BUG=skia:6046

Change-Id: I43676d28f82abf093ef801752f3a9e881580924c
Reviewed-on: https://skia-review.googlesource.com/5860
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Matt Sarett <msarett@google.com>
3 files changed