Check for zero offsets for PolyUtils

Bug: oss-fuzz:13202
Change-Id: Iee0ec8bdfe6345c91a584607cc499d69d227a919
Reviewed-on: https://skia-review.googlesource.com/c/194422
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
1 file changed