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