update libwebp to v1.3.1-1-g2af26267

2af26267 Fix OOB write in BuildHuffmanTable.
https://crbug.com/1479274

Change-Id: I56529150ce1250770ce10afc6279349b02520d93
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/753477
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
2 files changed