fix pathops coincidence fuzz bug

Simplifying a series of rects with very large bounds
triggers a coincidence bug where, after one of the
intersection points that marks a coincident range
has been deleted, it is referenced.

Both the deletion and reference is (probably) happening
in the SkOpCoincidence::AddExpanded() phase of
HandleCoincidence(), and may signify a bug that could
happen with usable input data, but I haven't been
able to determine that.

For now, abort the Simplify() when the erroneous
condition is detected.

TBR=reed@google.com
BUG=558281

Review URL: https://codereview.chromium.org/1463923002
2 files changed