Fix Perlin noise fuzz issue

The main "fix" here was that the assert was checking the un-clamped input value rather than the clamped value.

The SkValidatingReadBuffer.cpp change was required to get the reproducing fuzz test case to complete.

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2107453002

Review-Url: https://codereview.chromium.org/2107453002
2 files changed