[Bug Report] In multiple selection mode, Cascader reported an error (Press the backspace key repeatedly)

### Element UI version
2.15.12

### OS/Browsers version
Win10 / Chrome Version 107.0.5304.88 (Official version) (64-bit)

### Vue version
2.5.17

### Reproduction Link
https://codepen.io/chanspace/pen/mdKYgmY

### Steps to reproduce
In multiple selection mode:
1. First, you need to set both collapse-tags and filterable value is 'true',
2. Then, select a few options, And backspace a few more times,
3. The console will report an error: `Cannot read properties of undefined (reading 'getValueByOption')`

### What is Expected?
Do nothing but report no errors

### What is actually happening?
Component reported an error