Latte: fixed snippetArea with included template when snippetMode is disadled

When snippetArea contains included template then template was not rendered in non-ajax mode (when snippetMode is not enabled)
example code:
```smarty
{snippetArea foo}
{include "foo.latte"}
{/snippetArea}
```
(content of foo.latte was not rendered)

This fix seems to work, but I don't like it. Do you have a better idea how to fix it?