iconhelper: Store surface in ensure_surface()
iconhelper: Store surface in ensure_surface()

Do not assign it in the functions that actually load the surface. Make
those just return the surface.

grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita