Undirected multigraph edges are filled polygons in Matplotlib

[vnmabus]

Describe the bug
Plotting undirected multigraphs with the Matplotlib backend, the resulting image has filled edges.

To reproduce
Use the following code:

import igraph as ig
import matplotlib.pyplot as plt

g = ig.Graph([(0,1), (1,0), (1,2), (2,0)], directed=False)

fig, ax = plt.subplots()
ig.plot(g, target=ax)

This generates the following image:

Version information
I am using version 0.11.2 installed using pip.

[iosonofabio]

Thank you @vnmabus

I thought I had caught all cases but evidently I missed one. I'll make a PR over the weekend.

[iosonofabio]

I made a quick PR for this, it's under control and apologies for the incorrect behaviour.

If this passes CI and is merged quickly, we could consider a hotfix minor release, depending on @ntamas 's availability over the next few days.

[szhorvat]

I'd like a C release quite soon (one more PR to merge). Let's do the two releases together

[ntamas]

This is now fixed in 0.11.3, which will be on PyPI in a few hours or so.