Nested lists get removed

When going from visual mode to HTML, the inner nested lists get removed.

### Expected

```
<ul>
   <li>Item
   <ul>
      <li>Inner item</li>
   </ul>
   </li>
</ul>
```

### Observed

```
<ul>
   <li>Item</li>
</ul>Inner item
```

### Reproduced
1. Start with a nested list inside a list
2. Switch to visual mode
3. Switch back to HTML mode and notice the change