SkQP: fix Filterable.filter

Change-Id: Id50c24d16a3ba6810fbf49b91a7a93c3df5cb743
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/223296
Reviewed-by: Hal Canary <halcanary@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
1 file changed