wayland: Ensure to set gtk_surface dbus properties after hide()

Currently hiding destroys the wl_surface and all related interfaces,
(including the gtk_surface1) so the next time the GdkWindow is mapped,
we don't bother to set the DBus properties. Toggle the check off so
it's actually issued again after the GdkWindow gets a gtk_surface1.

https://bugzilla.gnome.org/show_bug.cgi?id=773686

gdk/wayland/gdkwindow-wayland.c

@@ -2528,6 +2528,7 @@ gdk_wayland_window_hide_surface (GdkWindow *window)
         {
           gtk_surface1_destroy (impl->display_server.gtk_surface);
           impl->display_server.gtk_surface = NULL;
+          impl->application.was_set = FALSE;
         }
 
       wl_surface_destroy (impl->display_server.wl_surface);