Fix initial position of X11 override-redirects

Presumably this fixes #228.  The position of the scene node for XWayland
override-redirect windows was never being set.

xwayland.h

@@ -13,6 +13,7 @@ struct cg_xwayland_view {
 	struct wl_listener unmap;
 	struct wl_listener map;
 	struct wl_listener request_fullscreen;
+	struct wl_listener set_geometry;
 };
 
 struct cg_xwayland_view *xwayland_view_from_view(struct cg_view *view);