Fix issue with offsetting polygon by 0 distance. Need to output matching indices as well. Bug: skia:13417, chromium:937412 Change-Id: I251a70eb07fda8b3a257d9f57ebdd9f20ad01b5a Reviewed-on: https://skia-review.googlesource.com/c/skia/+/197160 Reviewed-by: Kevin Lubick <kjlubick@google.com> Commit-Queue: Kevin Lubick <kjlubick@google.com> Commit-Queue: Jim Van Verth <jvanverth@google.com>