fix fuzzer bugs in pathops

one from clusterfuzz, one from Skia fuzzer

R=kjlubick@google.com
Bug:853938
Change-Id: If456bf45e4d75edecf4e4e8222ddcdaa301455f4
Reviewed-on: https://skia-review.googlesource.com/135701
Commit-Queue: Cary Clark <caryclark@skia.org>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Auto-Submit: Cary Clark <caryclark@skia.org>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
2 files changed