fixed editbox default text being pre-selected in some cases

Mostly noticed when using the command key "/", this happens because the irr::SEvent is a simple uninitialized struct and KeyInput.Shift is just a bitfield bit, resulting in an increased chance that the injected End-key (move cursor to end and remove selection) is seen as Shift-End (select text until the end).

The fix adds the missing inits to where this end-key trick is used - at least I hope I haven't overlooked any.