fix conic path fuzz

The test conic has a very large weight, so it reduces to a pair
of lines. Detect this case rather than subdividing the conic
so much that the answers are meaningless.

R=herb@google.com, reed@google.com
BUG=638223
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2268073004

Review-Url: https://codereview.chromium.org/2268073004
3 files changed