[bug report] when multiple drop-down components are selected and there are a lot of data selected, clear the selected items at this time, and the selected items will appear out of the box and then disappear

### Element UI version
2.15.3

### OS/Browsers version
chrome版本 91.0.4472.114（正式版本） (x86_64)

### Vue version
2.6.14

### Reproduction Link
https://codepen.io/mrretro/pen/jOmqMgd

### Steps to reproduce
下拉组件多选时，全选所有项后，点击清空选中，选中的ui会先跑出选择框外面再消失。

### What is Expected?
希望直接消失，不要出现出框行为。

### What is actually happening?
取消全选后，选中内容出框了。