Fix msan errors in webp decoder

Bug: skia:
Change-Id: I919a24fc61137c4a30160c97ad69fa4a2eadd031
Reviewed-on: https://skia-review.googlesource.com/10325
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
1 file changed