search: Defer updating results on allocation changes until redraw
Since the `notify::allocation` signal will obviously get emitted while
the actor is inside an allocation cycle and we might end up doing
changes to its allocation inside `updateSearch` by hiding or showing the
actor (which queues a relayout), we get a warning from Clutter.
Fix this by delaying the call to the parent method until the next
redraw, which should happen a few moments after the current relayout.