file chooser: Small cleanup
file chooser: Small cleanup

Ask the search model if it is empty, instead of maintaining this
information manually in the file chooser widget.

Adamovskiy/gtk,jigpu/gtk,Adamovskiy/gtk,alexlarsson/gtk,davidgumberg/gtk,jadahl/gtk,grubersjoe/adwaita,grubersjoe/adwaita,jadahl/gtk,jadahl/gtk,jadahl/gtk,Adamovskiy/gtk,Adamovskiy/gtk,grubersjoe/adwaita,chergert/gtk,grubersjoe/adwaita,chergert/gtk,grubersjoe/adwaita,chergert/gtk,alexlarsson/gtk,jigpu/gtk,chergert/gtk,alexlarsson/gtk,jigpu/gtk,grubersjoe/adwaita,Adamovskiy/gtk,jadahl/gtk,alexlarsson/gtk,jadahl/gtk,grubersjoe/adwaita,davidgumberg/gtk,davidgumberg/gtk,alexlarsson/gtk,jigpu/gtk,jigpu/gtk,alexlarsson/gtk,davidgumberg/gtk,chergert/gtk,Adamovskiy/gtk,davidgumberg/gtk,jadahl/gtk,alexlarsson/gtk,alexlarsson/gtk,jadahl/gtk,jigpu/gtk,Adamovskiy/gtk,chergert/gtk,davidgumberg/gtk,grubersjoe/adwaita,chergert/gtk,Adamovskiy/gtk,jigpu/gtk,chergert/gtk,davidgumberg/gtk,jigpu/gtk,davidgumberg/gtk