Simplify mask/clip intersection, making sure to explicitly check for an empty mask.

Previously we were only asserting the mask wasn't empty, which isn't necessarily true when we're given pathological float coordinates like +Inf or NaN.

A local run of nanobench --match text_ was not able to show this is faster or slower.

This patch fixed this first Chrome bug on my desktop, and the second is probably a dupe.
BUG=chromium:619378,chromium:613912

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2073873002

Review-Url: https://codereview.chromium.org/2073873002
2 files changed