Correct conversion from RGB to OkHsl when the total chrominance is very small. Previously, the output values would be set such that hue and saturation were 0 and luminance was based on conversion from RGB to Oklab, which is the correct behavior. However, this would be immediately overridden by calculating the conversion from Oklab to OkHsl using the new OkHsl values as input, resulting in black regardless of the correct luminance.
This MR prevents the second, bogus conversion from occurring.
Fixes #6228 (closed).