Nickserv logs a stack trace when a user quits

[Jeremy Thurgood]

Looks like we're trying to logout a user who no longer exists.

 Traceback (most recent call last):
   File "/var/lib/python-support/python2.5/axiom/store.py", line 1659, in transact
     result = f(*a, **k)
   File "/home/jerith/python/kali/trunk/kali/protocol.py", line 159, in handle
     method(prefix, *params)
   File "/home/jerith/python/kali/trunk/kali/protocol.py", line 178, in irc_QUIT
     self.services.event('quit', source, msg)
   File "/home/jerith/python/kali/trunk/kali/controller.py", line 338, in event
     self.sendEvent(p, event, *params)
 --- <exception caught here> ---
   File "/home/jerith/python/kali/trunk/kali/controller.py", line 349, in sendEvent
     method(*params)
   File "/home/jerith/python/kali/trunk/kali/nickserv.py", line 198, in event_quit
     self.logout(nick)
   File "/home/jerith/python/kali/trunk/kali/nickserv.py", line 161, in logout
     self.ctrl.getUser(nick).registered = False
 exceptions.AttributeError: 'NoneType' object has no attribute 'registered'

[Jeremy Thurgood (jerith)]

By the time NickServ gets the quit event, the user no longer exists. It should be safe to just drop the logout.