compositor: don't call role unmap hook without an object

include/wlr/types/wlr_compositor.h

@@ -87,6 +87,9 @@ struct wlr_surface_role {
 	void (*commit)(struct wlr_surface *surface);
 	/**
 	 * Called when the surface is unmapped. May be NULL.
+	 *
+	 * If the role is represented by an object, this is only called if
+	 * such object exists.
 	 */
 	void (*unmap)(struct wlr_surface *surface);
 	/**

types/wlr_compositor.c

@@ -752,7 +752,8 @@ void wlr_surface_unmap(struct wlr_surface *surface) {
 	}
 	surface->mapped = false;
 	wl_signal_emit_mutable(&surface->events.unmap, NULL);
-	if (surface->role != NULL && surface->role->unmap != NULL) {
+	if (surface->role != NULL && surface->role->unmap != NULL &&
+			(surface->role_data != NULL || surface->role->no_object)) {
 		surface->role->unmap(surface);
 	}