Fix how play_cmd() ensures connection close

Fix how play_cmd() ensures connection close

play_cmd() needs to return in a state that makes player_login() break
the login command loop.

play_cmd() assumes player_main() always returns in such a state:
connection's EOF indicator set.  Unfortunately, the assumption is
wrong.  Fortunately, play_cmd() checks it, oopses and recovers.

player_main() can return with neiter error nor EOF indicator set,
e.g. when the game is down.

player_main() can return with just the error indicator set.  For
instance, when the client dies, io_input() detects ECONNRESET, sets
the error indicator and fails.

Broken in commit 8549efbc.  Fix by setting the EOF indicator silently
(without oopsing) when necessary.