Fix regressions from search max results fix

Search doesn't work if no search provider other than the app search is enabled right now, this regressed with 1a27ff61. The code mentioned in this discussion was meant to handle this case, but I seem to have forgotten the reproducer for the problem back then.

The other issue this fixes is a The actor is currently inside an allocation cycle warning from Clutter that appeared because we can end up hiding and showing the actor from inside the notify::allocation handler.