Fixed minor bug where the memcached value for how many accounts an IP had

Fixed minor bug where the memcached value for how many accounts an IP had
created that day would be increased even if $wgAccountCreationThrottle was
hit. This meant if an IP hit the throttle and then the throttle was raised
later that day, the IP still couldn't create another account, because it
had marked them as having created another account, when their last account
creation had actually failed.