hpgl CP command omits second parameter

[Mittagskogel]

When using the CP command with a second parameter of 0.0, chiplotle incorrectly omits the second parameter in the HPGL output. This also causes the hp2xx converter to fail.

It looks like this can be fixed simply by changing this line in commands.py:
if self.spaces and self.lines:
to
if self.spaces != None and self.lines != None:

Thank you.