When the [bug report] El select component is placed in the label, clicking the tail arrow icon will trigger two click events, resulting in failure to expand

### Element UI version
2.13.0

### OS/Browsers version
chrome

### Vue version
2.6.11

### Reproduction Link
https://codepen.io/greenhandTan/pen/QWjgQaE

### Steps to reproduce
点击select右侧箭头，发现无法展开。demo中已附了修复方法

### What is Expected?
正常展开

### What is actually happening?
无法展开