call nLoginProcess::Finish in the foreground

nLoginProcess::Finish does not talk to the authority with blocking
requests, so it does not need to be run in a background thread.
(and if if would, ScheduleMayBlock would be the scheduler to use)

It does, however, in S_LoginResultCallback implemented in ePlayer.cpp,
send regular messages, which has to be done on the main thread.

Fixes https://github.com/ArmagetronAd/armagetronad/issues/1
(I hope, it's really just a best guess)