Avoid unstubbing $wgUser before the end of Setup.php in User::getBlockedStatus()

Avoid unstubbing $wgUser before the end of Setup.php in User::getBlockedStatus()

Autocreation needs to check if the current IP is blocked from account
creation.

There are two ways we could go here: treat $wgUser as logged-out, or
assume it will eventually be the user name specified by the session.
This patch chooses the former, by the logic that at this early point in
the setup process we don't have a logged-in user determined yet so no
username can really be considered to match the logged-in user.

Bug: T124367
Change-Id: I631bec85291b57f07c378cf6554a8f06cf3fb00c