Tighten up masking of colorType & alphaType in SkImageInfo serialization (for fuzzer bug)

In this case the int that contains the color and alpha types is getting munged. We don't really case that the surplus bits are 0 just that the values we care about are reasonable.

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2110493002

Review-Url: https://codereview.chromium.org/2110493002
1 file changed