Ensure default SkPaints w/ dither don't get dithered

Skipping dithering of const paints was originally added in:

https://skia-review.googlesource.com/c/skia/+/19880/

Change-Id: Icebca1c3ef779bb103030deac12621619f5ce248
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/437116
Reviewed-by: Florin Malita <fmalita@chromium.org>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
2 files changed