fix: fix FormItem required status error

[WangZhekun]

当FormItem表单项的校验规则为： [ { validator: (rule, value, callback) => { callback() }, trigger: 'blur' }, { required: true, message: 'Please fill in the user name', trigger: 'blur' } ]时，label前方的红*会丢失。复现见：https://run.iviewui.com/zw7u2Wri