check for zero scale in SkDraw::ComputeResScaleForStroking

If the transform used to compute the res scale has both 0 scale and skew,
then it will currently compute a 0 res scale. This causes getFillPath
to trigger an assertion while using SkStroke since that can't handle
a 0 res scale.

Downstream Firefox bug report: https://bugzilla.mozilla.org/show_bug.cgi?id=1284356

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2125933003

Review-Url: https://codereview.chromium.org/2125933003
1 file changed