fix fuzzers

Many old pathops-related fuzz failures have built up while
the codebase was under a state a flux. Now that the code
is stable, address these failures.

Most of the CL plumbs the debug global state to downstream
routines so that, if the data is not trusted (ala fuzzed)
the function can safely exit without asserting.

TBR=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2426173002

Review-Url: https://chromiumcodereview.appspot.com/2426173002
48 files changed