exit computeFilters if filter width is zero

The fuzzer associated with this bug triggered an assert
when building the resize filter. I can't tell if there
is a more fundemental bug here or not.

Checking for a zero-sized filter fixes the fuzzer.

R=fmalita@chromium.org
BUG=595856
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1810333002

Review URL: https://codereview.chromium.org/1810333002
1 file changed