Make SkBlend_optsTests fail rather than crash when resources are missing

BUG=skia:5314

TBR=herb@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1987143002

Review-Url: https://codereview.chromium.org/1987143002
1 file changed