Fixed error when normal.z = 1 in GPUs with binary16 floats

Check failed in GPUs with low-precision floats since 0.9999 was too small a difference from 1 to be detected by a 16-bit float comparison. Changed it to 0.999 which fixed the issue and results in indistinguishable correct behavior.

BUG=skia:5499
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2124183004

Review-Url: https://codereview.chromium.org/2124183004
1 file changed