Check for null colorFilter in FuzzCanvas

Follow up to https://skia-review.googlesource.com/c/skia/+/108300

Bug: skia:
Change-Id: I1b8b6ff71c71388660e09b3a7e8c77a40b1a1d12
Reviewed-on: https://skia-review.googlesource.com/108960
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
1 file changed