Update item focus even if it doesn't have a canvas

Update item focus even if it doesn't have a canvas

Currently the item focus data is not updated if it is not in a canvas.
This means a subFocusItem may be deleted when the item is outside of a
canvas, creating a stale pointer when the item is moved back into a
canvas.

This change also means that the last item to set focus=true will now
consistently get activeFocus. Previously if an item did not have a
canvas and then was moved back into the canvas, the first item found
with focus=true would get activeFocus.

Task-number: QTBUG-24616
Change-Id: Ia706bd6ba6bcbccd616b5019c7c0fae4c39afa7f
Reviewed-by: Andrew den Exter <andrew.den-exter@nokia.com>