fix fuzzer bug

Fix another fuzzer bug.

Some PathOps asserts only make sense if the incoming data is
well-behaved. Well-behaved tests set debugging state to
trigger these additional asserts.

Formalize this by creating macros similar to SkASSERT that
check to see if the assert should be skipped.

TBR=reed@google.com
BUG=629962
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2169863002

Review-Url: https://codereview.chromium.org/2169863002
8 files changed