fix fuzzer bugs

Add a couple more cases where Op() fails and
returns false when the out of range input
values make the internal numeric unstable.

TBR=reed@google.com
BUG=647834, 648068
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2348263002

Review-Url: https://codereview.chromium.org/2348263002
2 files changed