[Draw] qcurv doesn't work, at all

[hiiamboris]

Describe the bug

What do the docs say:

So, essentially, qcurv, in contrast to other shape curve functions, can only accept one point (1).
Let's try it in 3 different ways...

view [
	base 250x250 draw [		; feeding a single point
		scale 10 10 pen linear cyan purple 
		shape [move 5x5 qcurv 20x5 qcurv 20x20 qcurv 5x20 qcurv 5x5 move 5x5]
	] 
	base 250x250 draw [		; feeding pairs of points
		scale 10 10 pen linear cyan purple 
		shape [move 5x5 qcurv 20x5 20x20 qcurv 5x20 5x5 move 5x5]
	] 
	base 250x250 draw [		; feeding a bunch
		scale 10 10 pen linear cyan purple 
		shape [move 5x5 qcurv 20x5 20x20 5x20 5x5 move 5x5]
	] 
]

Some nice smoothing (2) ☻

Expected behavior

(1) bug in the docs - should accept multiple points
(2) behavior of R2 is desired - here's the R2 script version and the R2 result:

view layout [
	across
	box 250x250 effect [draw [
		scale 10 10 pen red
		shape [move 5x5 qcurv 20x5 qcurv 20x20 qcurv 5x20 qcurv 5x5 move 5x5]
	]]
	box 250x250 effect [draw [
		scale 10 10 pen red
		shape [move 5x5 qcurv 20x5 20x20 qcurv 5x20 5x5 move 5x5]
	]]
	box 250x250 effect [draw [
		scale 10 10 pen red
		shape [move 5x5 qcurv 20x5 20x20 5x20 5x5 move 5x5]
	]]
]

Platform version (please complete the following information)

Red 0.6.4 for Windows built 30-Jan-2019/9:03:13+03:00 commit #25ef631

[hiiamboris]

There actually is one scenario where it does work, albeit only once. After qcurve.

view [
	base 250x250 draw [
		scale 10 10 pen linear cyan purple 
		shape [move 5x5 qcurve 20x5 20x20 qcurv 5x20 qcurv 5x5]
	] 
	base 250x250 draw [
		scale 10 10 pen linear cyan purple 
		shape [move 5x5 qcurve 20x5 20x20 qcurv 5x20 5x5]
	] 
]

While the same code in R2 - qcurv can continue the curve indefinitely:

view layout [
	across
	box 250x250 effect [draw [
		scale 10 10 pen red
		shape [move 5x5 qcurve 20x5 20x20 qcurv 5x20 5x5]
	]]
	box 250x250 effect [draw [
		scale 10 10 pen red
		shape [move 5x5 qcurve 20x5 20x20 qcurv 5x20 qcurv 5x5]
	]]
]