Fix reflected ovals.

Fix reflected ovals.

Addresses an issue with ovals transformed by a matrix with a reflection.
Also adds a further check for circles to ensure that teeny tiny ovals
(sizes < SK_ScalarNearlyZero) aren't treated as circles.

Change-Id: Ie50e4a98365eba7c23e53e68886ebac981ed1def
Reviewed-on: https://skia-review.googlesource.com/13989
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>