listbox: keep emitting ::row-selected
listbox: keep emitting ::row-selected

This was accidentally lost when multi-selection was added, causing
sidebars like the one in gnome-contacts or polari to not work any
more.

grubersjoe/adwaita,davidgumberg/gtk,chergert/gtk,jadahl/gtk,jadahl/gtk,chergert/gtk,grubersjoe/adwaita,ahodesuka/gtk,grubersjoe/adwaita,jessevdk/gtk,ahodesuka/gtk,msteinert/gtk,Adamovskiy/gtk,Lyude/gtk-,davidgumberg/gtk,Sidnioulz/SandboxGtk,Lyude/gtk-,Lyude/gtk-,jigpu/gtk,jadahl/gtk,jadahl/gtk,jigpu/gtk,Sidnioulz/SandboxGtk,Sidnioulz/SandboxGtk,Sidnioulz/SandboxGtk,alexlarsson/gtk,ahodesuka/gtk,jessevdk/gtk,Sidnioulz/SandboxGtk,Adamovskiy/gtk,alexlarsson/gtk,jessevdk/gtk,ahodesuka/gtk,jadahl/gtk,grubersjoe/adwaita,msteinert/gtk,davidgumberg/gtk,davidgumberg/gtk,jigpu/gtk,chergert/gtk,ahodesuka/gtk,Lyude/gtk-,davidgumberg/gtk,Adamovskiy/gtk,jadahl/gtk,alexlarsson/gtk,chergert/gtk,msteinert/gtk,jadahl/gtk,Adamovskiy/gtk,jessevdk/gtk,chergert/gtk,jessevdk/gtk,Adamovskiy/gtk,chergert/gtk,Lyude/gtk-,ahodesuka/gtk,msteinert/gtk,Lyude/gtk-,Lyude/gtk-,Adamovskiy/gtk,jessevdk/gtk,grubersjoe/adwaita,jigpu/gtk,grubersjoe/adwaita,jigpu/gtk,alexlarsson/gtk,jessevdk/gtk,davidgumberg/gtk,grubersjoe/adwaita,Sidnioulz/SandboxGtk,alexlarsson/gtk,jigpu/gtk,alexlarsson/gtk,davidgumberg/gtk,msteinert/gtk,chergert/gtk,Adamovskiy/gtk,jadahl/gtk,ahodesuka/gtk,chergert/gtk,Adamovskiy/gtk,msteinert/gtk,Lyude/gtk-,davidgumberg/gtk,ahodesuka/gtk,jigpu/gtk,alexlarsson/gtk,alexlarsson/gtk,grubersjoe/adwaita,jigpu/gtk