plugins/overview: also do things when changing to active
We were binding to the statusChanged signal, but then only doing anything if the status had changed to "Activating". This did not work for when the effect was activated without a gesture, because then its status would change straight to "Activated", bypassing the in-between state of "Activating."
This fixes clearing the search text on activation without a gesture.
Alternative to !4186 (closed).