Search bar not working properly in specific notes in book mode

### Is this a hackmd.io issue?

- [x] Yes, the bug happens on https://hackmd.io

### What's the problem

I encountered a case where the search bar doesn't properly filter the nodes in a specific book mode note:

#### Current behaviour


Provide steps to reproduce:

1. Go to
2. Click on the search bar on the top-left of the page
3. Enter `value` as the search keyword
4. See error

#### Expected behaviour

Nodes properly filtered according to the inputted keyword

#### Environment

I use HackMD on:

- OS: Ubuntu 22.04 LTS AMD64
- Browser: Mozilla Firefox
- Browser Version: 113.0.1