Add a test to ensure that a case where SkCubicClipper::ChopMonoAtY returns false is handled properly.

Also fixes a style issue in the fix for the issue being tested.

BUG=chromium:613918
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2021343004

Review-Url: https://codereview.chromium.org/2021343004
2 files changed