PlotingExtension.sub inconsistency

[rustonaut]

When skimming the code I noticed that there is a Bug wrt. the self.sub field

It is assigned in the constructor with:

self.sub = self._start_server_process() if self.start_server else None

but _start_server_process does not return anything but set's self.sub = ... which is then overwritten with its non existing return value (aka. None)

Also self.sub isn't used anywhere

Open questions?

• only add a self._sub attribute if it has a sub?

Note this is a pretty minor bug, and this is a class which probably gets completely rewritten anyway

[rustonaut]

no explicit self.sub assignment is done in the __setstate__ method.

[dmitriy-serdyuk]

This should be fixed with #35.