Fix fuzzer bug

BUG=663687

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4580

Change-Id: I9e914a1134b8049cf62bb36d4a6145eb8487d4e6
Reviewed-on: https://skia-review.googlesource.com/4580
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
1 file changed