[Bug Report] el-select component is enabled (automatic-dropdown) property is not normal

### Element UI version
2.13.2

### OS/Browsers version
win10_1909 Edge_81.0.416.64

### Vue version
2.6.11

### Reproduction Link
https://codepen.io/xiaofan007/pen/KKdJKzP?editable=true%3Dhttps%3A%2F%2Felement.eleme.cn%2F

### Steps to reproduce
Mouse click on the el-select component with enabled 'automatic-dropdown' property

### What is Expected?
The drop-down box displays normally when the el-select component enables the "auto drop-down" property.

### What is actually happening?
When the el-select component is enabled 'automatic-dropdown' property, the first click on the component is not normal, and it will be displayed normally only when it is clicked again is enabled.