[Bug Report] Table header can't horizontal scrolling when body is empty

### Element UI version
2.11.1

### OS/Browsers version
Windows10 / Chrome 76.0.3809.100

### Vue version
2.6.10

### Reproduction Link
https://codepen.io/cyse-ars/pen/QemvVz?&editable=true

### Steps to reproduce
1. Scroll right end.
2. Filters rows that body to be empty. (reproduction link's filter will become always empty)

### What is Expected?
Shows table header and horizontal scrollbar.
Keep scroll position.

### What is actually happening?
Horizontal scrollbar is not shown, and mouse scrolling is not working.
Scroll position goes back to left end.

So if UI has no button to reset filter, that is no way to restore filtered dataset.