draw_points argument in PolylineArtist not functional

[tkmmark]

Consider making the following insertions (as highlighted):

For the developers' copy-and-paste-convenience, the code has been reproduced here as text:

self._points_artists = []

if self._draw_points: for point in self.polyline: self._points_artists.append(self.plotter.add(point))

Setup is based on LineArtist... and tested, as shown below: