fix more chrome asan fuzzer failures

Small change to gracefully quit
when fuzzer values cause pathops
to fail.

TBR=reed@google.com
BUG=657411, 657559
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2426393004

Review-Url: https://chromiumcodereview.appspot.com/2426393004
4 files changed