Do not allow port 0
Do not allow port 0

Attackers injected node addresses with port 0 into the network. Port 0
is unusable on many OSes and can't be listened on. PyBitmessage won't
accept nodes that have port 0 anymore.

debguy0x/PyBitmessage,timothyparez/PyBitmessage,torifier/PyBitmessage,debguy0x/PyBitmessage,torifier/PyBitmessage,hb9kns/PyBitmessage,bmng-dev/PyBitmessage,debguy0x/PyBitmessage,torifier/PyBitmessage,hb9kns/PyBitmessage,timothyparez/PyBitmessage,hb9kns/PyBitmessage,bmng-dev/PyBitmessage,hb9kns/PyBitmessage,bmng-dev/PyBitmessage,debguy0x/PyBitmessage,timothyparez/PyBitmessage,timothyparez/PyBitmessage,torifier/PyBitmessage