inspector: Set statistics button sensitivity
inspector: Set statistics button sensitivity

After moving the button the header, it is now visible when
statistics are not available. Disable it in this case.

alexlarsson/gtk,ahodesuka/gtk,jigpu/gtk,Lyude/gtk-,davidgumberg/gtk,alexlarsson/gtk,grubersjoe/adwaita,alexlarsson/gtk,ahodesuka/gtk,ahodesuka/gtk,chergert/gtk,jigpu/gtk,Adamovskiy/gtk,jigpu/gtk,chergert/gtk,davidgumberg/gtk,chergert/gtk,grubersjoe/adwaita,jadahl/gtk,chergert/gtk,Lyude/gtk-,jigpu/gtk,davidgumberg/gtk,Lyude/gtk-,jigpu/gtk,alexlarsson/gtk,grubersjoe/adwaita,davidgumberg/gtk,ahodesuka/gtk,Adamovskiy/gtk,davidgumberg/gtk,chergert/gtk,grubersjoe/adwaita,Lyude/gtk-,jadahl/gtk,Lyude/gtk-,grubersjoe/adwaita,grubersjoe/adwaita,Adamovskiy/gtk,jadahl/gtk,alexlarsson/gtk,grubersjoe/adwaita,Lyude/gtk-,chergert/gtk,alexlarsson/gtk,ahodesuka/gtk,jadahl/gtk,ahodesuka/gtk,ahodesuka/gtk,jigpu/gtk,Lyude/gtk-,jadahl/gtk,jadahl/gtk,jadahl/gtk,alexlarsson/gtk,grubersjoe/adwaita,jigpu/gtk,davidgumberg/gtk,Adamovskiy/gtk,chergert/gtk,chergert/gtk,Lyude/gtk-,ahodesuka/gtk,davidgumberg/gtk,Adamovskiy/gtk,jadahl/gtk,jigpu/gtk,Adamovskiy/gtk,Adamovskiy/gtk,Adamovskiy/gtk,alexlarsson/gtk,davidgumberg/gtk