fix fuzzer

abort if incoming data is out of range

TBR=reed@google.com
BUG=676866

Change-Id: I7d4850611654a399e32ea2012b23ca369dc53e70
Reviewed-on: https://skia-review.googlesource.com/6525
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Cary Clark <caryclark@google.com>
2 files changed