contact: Initialize contact state properly

contact: Initialize contact state properly

A country must always be in contact of itself when option HIDDEN is
enabled.  The code ensures this by establishing contact whenever a
player logs in, in init_nats().  This is not the proper place.  Game
state should be initialized in empfile's oninit() callback, in this
case nat_oninit().  Do that, and drop the putcontact() from
init_nats().

Note that option LOSE_CONTACT only affects contact to other countries:
agecontact() doesn't age the country's contact to itself.

Use the opportunity to initialize contact so that getcontact() works
even when HIDDEN is disabled.  Just cleanup, it isn't actually called
then.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>