join queue: fix 2 bugs that could result in too many players on a team

join queue: fix 2 bugs that could result in too many players on a team

Join(): when a client queued for red, then a blue player left the team,
then a client (re)joined blue, the client queued for red was joined too
(stacking red team). Fixed by only joining queued players in Join() when
teams are currently balanced (the unbalanced cases are handled by
TeamBalance_QueuedPlayersTagIn()).

ClientKill_Now_TeamChange(): when all queued client(s) chose specific
team(s) and the last client (which skips the queue and triggers the
joins) chose autoselect from the team selection UI, it was possible they
were assigned the same team as one of the queued clients.  Fixed by
deferring the autoselect to Join() when needed/possible.