Fix fuzzer-found deserialization bug in SkPathRef

[Cherry pick of 0735de67c8a0812ae2fd103ae1bd7f2157c6a0b2 to chrome/m49.]

This fixes a bug in SkPathRef::CreateFromBuffer found by
fuzzing SkPaintImageFilter.

BUG=582705
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1653003004

Review URL: https://codereview.chromium.org/1653003004
NOTREECHECKS=true
NOTRY=true
NOPRESUBMIT=true

Review URL: https://codereview.chromium.org/1665613003
1 file changed