Improved server_get_network(): if we don't have the current network in the
network list use the server name in received in event 005.
(This fixes the problem that the network (%n) in the log file names would be
"NETWORK" instead of the real network name (this happened if the network was
not in the network list).)
Merge pull request #625 from orium/network-name-improve

Improved server_get_network()