handle polygon draw case where start point equals end point

[fs-99]

Thank you for the nice library, I'm using it mostly for basic draw calls.
I stumbled upon this when drawing shapes with randomly generated points, where I don't really care if this backend adds the endpoint for the last line or if I randomly generated the same end point as the start point.

[fs-99]

I forgot to change the docs: should I just remove the point about open paths or should I say "This supports both open and closed paths, i.e. the first and last points can be the same but don't have to."

[ripytide]

Looks useful, I would change the docs to say that it supports open and closed paths and that if the last point is not equal to the first then the path is closed anyway.

[theotherphil]

Seems like reasonable behaviour if clearly documented. Thanks, I’ll merge after the docs are updated to explain the new behaviour.

[fs-99]

Done. (and @ripytide I gave it the names, the length is already checked if that was your point)

[theotherphil]

Thanks!