ActiveUsersPager: Fix ordering and return 0-action users
Ia9d2ff00 introduced two incompatibilities with what the base classes
were trying to do:
* The $descending flag passed to buildQueryInfo() does not actually mean
DESC if $this->mIsBackwards is set. The old code just blindly assumed
that was the case.
* For paging to work right, we must return all $limit rows, we can't
filter out users with 0 actions. Thus we need to LEFT JOIN
recentchanges (and move some conditions around to cope)..
Bug: T217525
Change-Id: Iba105a31ff61fbb14931bf8903538bfe7b0ba48b