Return to lobby if preferences unavailable

What the title says!
Combine the 3 loops for the 3 seperate options into one loop.
eg:
```
for(var/mob/new_player/player in unassigned)
    switch(player.client.prefs.alternate_option)
        if(BE_ASSISTANT)
           X
        if(RETURN_TO_LOBBY)
           Y
```