evas - smart obj - set smart data to null after del func to avoid bugs

so smart data get cleanly returns null ... set it to nukll after del
func called as now the smart data shiuld be gone and not usable
anymore. this means we dont return junk smart data if called after this.

@fix

src/lib/evas/canvas/evas_object_smart.c

@@ -1462,6 +1462,7 @@ evas_object_smart_del(Evas_Object *eo_obj)
    free(sobj->interface_privates);
    sobj->interface_privates = NULL;
 
+   sobj->data = NULL;
    if (s) evas_object_smart_unuse(s);
 }