[Bug report] Cannot read properties of undefined (reading 'length')

[xdewx]

Describe the bug
调用setMarkdown后，在编辑框内无法继续输入，控制台提示：

cherry-markdown.core.js:1 
        
       Uncaught TypeError: Cannot read properties of undefined (reading 'length')
    at kn2 (cherry-markdown.core.js:1:77288)
    at Ln2 (cherry-markdown.core.js:1:78003)
    at jn2 (cherry-markdown.core.js:1:82781)
    at vr2 (cherry-markdown.core.js:1:89638)
    at mr2 (cherry-markdown.core.js:1:89575)
    at Vo2.prepareSelection (cherry-markdown.core.js:1:192796)
    at zr2 (cherry-markdown.core.js:1:103088)
    at cherry-markdown.core.js:1:101808
    at cherry-markdown.core.js:1:101888
    at cherry-markdown.core.js:1:101612

另外可以观察到的是：

1. setMarkdown后游标的位置和文本位置不一致，如图
   

To Reproduce
Steps to reproduce the behavior:

1. init
2. setMarkdown

Expected behavior
在setMarkdown后可以继续正常输入

Environment (please complete the following information):

• OS: linux
• Browser : edge
• Version：0.8.14

[xdewx]

从这里找到了解决方式