Unbreak activating a search provider result

I swear I had tested it before pushing, but looks I made a mistake.

We have to create the main window before setting the active item.
Otherwise the emission of PhotosItemManager::active-changed will be
missed. Secondly, since we are not moving from a view with an
associated model we should skip setting it.

Fallout from 5e6a86718aabf7731f885adcaf5b7ef4da905d3b

Fixes: https://bugzilla.gnome.org/725328