Fix cusp detection for linear cubics in FindCubicConvex180Chops

There are two types of linear cubics, one that turns back on itself
and one that maintains a consistent tangent direction. The latter
should not have cusps added.

Bug: b/433057370
Change-Id: Idb5c0ff120e5568b61c2c926db1bf2b2c524d21d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1028236
Reviewed-by: Thomas Smith <thomsmit@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
2 files changed