Fix Color Lines with a single color stop, and multiple stops all at the same stop offset

[justvanrossum]

See also the comment here:

black-renderer/Lib/blackrenderer/font.py

Lines 395 to 419 in 9718f42

	def _normalizeColorLine(colorLine):
	stops = [stopOffset for stopOffset, color in colorLine]
	minStop = min(stops)
	maxStop = max(stops)
	if minStop != maxStop:
	stopExtent = maxStop - minStop
	colorLine = [
	((stopOffset - minStop) / stopExtent, color)
	for stopOffset, color in colorLine
	]
	else:
	# Degenerate case. minStop and maxStop are used to reposition
	# the gradients parameters (points, radii, angles), through
	# interpolation. By setting minStop and maxStop to 0 and 1,
	# we at least won't mess up the parameters.
	# FIXME: should the gradient simply not be drawn in this case?
	# 1. If there's only one color stop, we can just draw a solid
	# color.
	# 2. If there are > 1 color stops all at the same color stop
	# offset, things get interesting: everything "to the left"
	# should get color[0], everything "to the right" should get
	# color[-1]. If there are more than 2 color stops, all but the
	# first and last should be ignored.
	minStop, maxStop = 0, 1
	return minStop, maxStop, colorLine