Fix FuzzCanvas imageFilter selection

We never updated the index range when AlphaThreshold was removed, so
many fuzzers would assert in debug builds.

Change-Id: I6a2032ca9515fcd8556ee13cdff87cbab135da62
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/714059
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed