Fix player thread race with update_init()

start_server() creates the thread running player_accept() before it
calls update_init().  However, update_init() initializes stuff used to
player threads: update_time[] and play_lock.  In theory, a player
thread could start before that, and crash when taking the
uninitialized play_lock.

Delay starting that tread until after update_init().

src/server/main.c

@@ -375,10 +375,9 @@ start_server(int flags)
     if (journal_startup() < 0)
 	exit(1);
 
-    empth_create(player_accept, 50 * 1024, flags, "AcceptPlayers", NULL);
-
     market_init();
     update_init();
+    empth_create(player_accept, 50 * 1024, flags, "AcceptPlayers", NULL);
 }
 
 /*