RateLimit: fix error on @get with nonexistent user

[ghost]

this can happen if a user that had rate limits set up got unregistered.

[progval]

The try block is a little too wide. eg. it would catch KeyError raised by an incorrect translation of the string in format_ratelimit.

Could you rewrite it like this?

                try:
                    user = ircdb.users.getUser(record.user)
                except KeyError:  # nonexistent user
                    continue
                else:
                    users.append('%s: %s' % (user.name,
                                             format_ratelimit(record)))