Wrap to <li/> only if element is't <li/>

In some cases, it's not necessary to wrap element in ```<li/>```. For example with this modelView:

```javascript
var view = new Backbone.View.extend({
   tagName: 'li',
   render: function() {
      this.$el.html('some text');
   }
});
```

Rendered DOM will be:

```html
<ul>
  <li data-model-cid="1">
    <li>some text</li>
  </li>
</ul>
```
So, my patch checks if we already have ```<li/>``` and only adds "data" attribute.