Fix some overflowing integers in SkPolyUtils

Bug: oss-fuzz:10293
Change-Id: If3a98e60081ebef7bdc8460fce4fa682245c68cc
Reviewed-on: https://skia-review.googlesource.com/153661
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
1 file changed