fix fuzzers

Two crashes and a hang. Abort and return false
in these cases.

TBR=kjlubick@google.com
BUG=skia:5983

Change-Id: I41ac3e56d47ee423b634b2f4886085b9caada76b
Reviewed-on: https://skia-review.googlesource.com/5716
Reviewed-by: Cary Clark <caryclark@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Cary Clark <caryclark@google.com>
2 files changed