[Bug Report] Select component popper option is in the wrong position

### Element UI version
2.13.1

### OS/Browsers version
Chrome

### Vue version
2.6.10

### Reproduction Link
https://jsfiddle.net/zwcp8d6u/

### Steps to reproduce
1. Focus on select component
2. type `M` and wait for remote search data
3. blur out of component
4. Focus on select component again
5. type `M` and wait for remote search data

### What is Expected?
Popper option appear on top of select component.

The popper option is in the right position

### What is actually happening?
Popper option appear on under of select component.

The popper option is in the wrong position. Causing to not see all the information