Wrong nesting of the output when calling getHtml method on item list

When calling the getHtml() method on a unordered list from a StructuredText field the list the first element is wrongfully rendered as a sibling of its expected parent (```<ul>```);

```php
$document->getHtml("local_product.ksps")
```

Raw output of the function :
```html
<li>Chaudière murale gaz à condensation à très haut rendement</li><ul><li>Chaudière double service, avec ballon eau chaude sanitaire 62 litres</li><li>Echangeur en acier inoxydable auto-nettoyant: résistance sans pareille à la corrosion</li><li>Brûleur à pré-mélange, gaz naturel ou propane</li><li>Avec vase d’expansion 12 litres</li><li>Raccordement ventouse en standard</li><li>Kits hydrauliques et accessoires de régulation en option</li></ul>
```

Note that the ```<ul>``` tag start **after** the first ```<li>``` element.

I saw no test in the suite adressing this specific use case. It should be fairly easy to reproduce.

Similar problem arises with ordered lists. Feels free to ask me to file a new issue.

![Screenshot of the API browser](https://cloud.githubusercontent.com/assets/201714/2987722/5a3f303c-dc51-11e3-9d06-33c1332c6556.png)