Fixed a skirmish arena queue bug

Fixed a skirmish arena queue bug where the arena launched when you were only 2 in the queue (so 1v1).
Now works properly : it wait for four players to tag 2v2 (six to 3v3) before launching one(for rated too).
It didn't affect rated because queue was only in a full group, so there were never only 2 people in the queue.