fix pathops coincidence fuzz bug

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
Committed: https://skia.googlesource.com/skia/+/1c9ce610501b7b864617356aeda12cd0caebe066

[caryclark, 2015-11-20 21:19:01]

The CQ bit was checked by caryclark@google.com

[commit-bot: I haz the power, 2015-11-20 21:19:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1463923002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1463923002/1

[commit-bot: I haz the power, 2015-11-20 22:06:31]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/1c9ce610501b7b864617356aeda12cd0caebe066