Fix AllocedProxyTest on Mesa

Mesa is handing us a context that supports MSAA but has 0 as the max number of color samples

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1967503004

Review-Url: https://codereview.chromium.org/1967503004
1 file changed