Fix invalid switch in FuzzCanvas

Also tweak when we report OOM - AFL-fuzz is fine, but libfuzzer should
abort, not exit.

Bug: skia:
Change-Id: Ic19277bbceec5e7c0ac966d6d9ac677bcfebcfae
Reviewed-on: https://skia-review.googlesource.com/93201
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Hal Canary <halcanary@google.com>
3 files changed