[TwigBundle] moved Form extension initialization as late as possible
[TwigBundle] moved Form extension initialization as late as possible

Because

 * it's better for performance (no need to init form templates if there is no forms)
 * right now, it crashes for all renderer except HTML (because the form templates obviously only exist for the HTML renderer)

The only other possible fix would be to force those resources to always use the HTML renderer

symfony/twig-bundle,symfony/twig-bundle