The last empty in code block disappear


### Versions

Step 1: write test file bellow:

```md
### test file

\```js
const a = 'b'

\```

there is an empty after `const a = 'b'`
```

Step 2: change to source code mode and change back.


Expect

Last blank line is reserved

Actually

The last line disappear







- Mark Text: 0.15.0
- Operating system: Windows 7
