iconhelper: clear the surface on invalidation
iconhelper: clear the surface on invalidation

This was missed during the pixbuf->surface conversion, so when the state
changed we were not recreating a new surface for it.

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