Fix failed filter followed by an affects-transparent-black filter.

When an upstream filter returns null, either through failure or clipping, a downstream affects-transparent-black
filter should still produce non-transparent pixels.

This patch fixes SkColorFilterImageFilter.

Note: this will affect the results of the imagefilterscropexpand GM.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1844593002

Review URL: https://codereview.chromium.org/1844593002
2 files changed