SkRegion: Do not assume good input.

BUG=chromium:873051

Change-Id: I2b84bade333e101fade81994203640ddf724f550
Reviewed-on: https://skia-review.googlesource.com/147041
Auto-Submit: Hal Canary <halcanary@google.com>
Commit-Queue: Cary Clark <caryclark@google.com>
Reviewed-by: Cary Clark <caryclark@google.com>
2 files changed