Scaling by zero should not produce blank

Something like this:

scaled(circle(5), 1, 0)

currently produces a blank image. However, this should be exactly the same set of points as

polyline([(-5, 0), (5, 0)])

which is drawn as a non-blank picture.

Start by reproducing the issue with scaled(circle(5), 1, 0) and compare it with polyline([(-5, 0), (5, 0)]). Trace the scaled and polyline entry points to determine why zero scaling becomes blank; done means both expressions render the same non-blank set of points.

索引モデルが issue の本文から書いたものです。