fix(obj): avoid to init NULL obj

See #6541

Signed-off-by: Sunrisepeak <speakshen@163.com>

src/core/lv_obj_class.c

@@ -102,6 +102,8 @@ lv_obj_t * lv_obj_class_create_obj(const lv_obj_class_t * class_p, lv_obj_t * pa
 
 void lv_obj_class_init_obj(lv_obj_t * obj)
 {
+    if(obj == NULL) return;
+
     lv_obj_mark_layout_as_dirty(obj);
     lv_obj_enable_style_refresh(false);