saturate some irect ops for fuzzers

Bug: skia:
Change-Id: I1c4f879a455048652abb619814841cd687a0474a
Reviewed-on: https://skia-review.googlesource.com/101881
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Reed <reed@google.com>
4 files changed