Fix some fuzzer bugs from Skia's image filter fuzzer

Change-Id: I432b3a351eecca0d36635e37f91d32c0e281b7d9
Reviewed-on: https://skia-review.googlesource.com/98384
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Reed <reed@google.com>
5 files changed