Fix quad type detection from SkPoint array

Change-Id: I2ea208f58845634ef25cf8f0395673c11fecf0dc
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/209169
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>