fix(obj): check obj->is_deleting at the beginning of obj_del_core (#4525)

Signed-off-by: wangxuedong <wangxuedong@xiaomi.com>

src/core/lv_obj_tree.c

@@ -372,12 +372,15 @@ static void lv_obj_del_async_cb(void * obj)
 
 static void obj_del_core(lv_obj_t * obj)
 {
+    if(obj->is_deleting)
+        return;
+
+    obj->is_deleting = true;
+
     /*Let the user free the resources used in `LV_EVENT_DELETE`*/
     lv_res_t res = lv_obj_send_event(obj, LV_EVENT_DELETE, NULL);
     if(res == LV_RES_INV) return;
 
-    obj->is_deleting = true;
-
     /*Clean registered event_cb*/
     uint32_t event_cnt = lv_obj_get_event_count(obj);
     for(uint32_t i = 0; i < event_cnt; i++) {