Add missing return type
Add missing return type

Pointed out by Chun-wei Fan
https://bugzilla.gnome.org/show_bug.cgi?id=640992

Unity-Technologies/gtk,Distrotech/gtk,Distrotech/gtk,johne53/MB3Gtk-2,Unity-Technologies/gtk,johne53/MB3Gtk-2,Distrotech/gtk,Distrotech/gtk,johne53/MB3Gtk-2,Unity-Technologies/gtk,johne53/MB3Gtk-2,Unity-Technologies/gtk,johne53/MB3Gtk-2,Unity-Technologies/gtk,Distrotech/gtk