Brought back TAB to switch team/all chat when nothing has been typed yet

The new ALT hotkey from https://github.com/OpenRA/OpenRA/pull/6281 is driving me nuts. When you have not typed anything and therefore nothing can be auto-completed, this will allow you to still use it to switch team and public chat.
That doesn't work when two people have nicks with the same length and the same starting letter(s). It then both auto-completes and switches between chat and team-chat.