Colors interpolated with 'hcl' colorSpace disappear.

[stevage]

mapbox-gl-js version: 0.42.2

Steps to Trigger Behavior

1. Set up a layer of points that interpolates in the 'hcl' colorspace from 'red' to 'blue

Expected Behavior

Every point renders some color, probably shades of purple, similar to with 'rgb' colorSpace:

https://codepen.io/stevebennett/pen/pdYmwq

Actual Behavior

Some points don't render at all.

https://codepen.io/stevebennett/pen/OOqYpz

I imagine that what's happening is the interpolation is pushing the colors outside the colorspace, maybe generating non-sensible colors. But I don't think the user ever wants invisible colors.

Side note: it's slightly frustrating that colors are specified as HSL, but can't be interpolated in HSL. The interpolation from hsl(0, 100%, 50%) to hsl(240, 100%, 50%) should be really clear, but presumably in HCL colorspace it is, um, 'clear' in a different sense.

[jfirebaugh]

This regressed in 670108d.