Some assert fixes for running the Fuzzer sample in GPU mode.

Some assert fixes for running the Fuzzer sample in GPU mode.

quadraticPointCount, cubicPointCount: passing NaN to GrNextPow2 causes
it to assert, so detect that and return the max points per curve
instead.

Passing a zero scale to GrStyle::applyToPath() makes it assert, so
draw nothing (likely what drawing with a zero scale is going to do
anyway).

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2257423002

Review-Url: https://codereview.chromium.org/2257423002