Don't allow iteration through non-finite points.

Added a unit test too.

BUG=chromium:756563

Change-Id: Ic77a89b4a98d1a553877af9807a3d3bdcd077bb9
Reviewed-on: https://skia-review.googlesource.com/44420
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Reed <reed@google.com>
3 files changed