Without this patch, `python main.py abc aabbcc milk` will reliably crash.
I believe what happens here is that we initialize all the slipnodes and
everything, and then `slipnet.predecessor` becomes `None`, which means
that if that concept ever arises on its own (vs. arising as the "opposite"
of "successor"), we'll be passing around `None` instead of a proper `Slipnode`
and everything goes sideways.
This line doesn't correspond obviously to anything in the Java code,
so I think it's just bogus --- an experiment in "brain damage" that was
accidentally committed?
