fix fuzz with null check

TBR=reed@google.com
BUG=skia:5819

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2925

Change-Id: I1957d3f8f5c78bed41bb7fe413ae870df24f7c50
Reviewed-on: https://skia-review.googlesource.com/2925
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Cary Clark <caryclark@google.com>
2 files changed