bug #1332 Fixing TwigServiceProvider when used with FormServiceProvider but without CsrfServiceProvider (skalpa)

This PR was merged into the 2.0.x-dev branch.

Discussion
----------

Fixing TwigServiceProvider when used with FormServiceProvider but without CsrfServiceProvider

Trivial fix for #1331, with test.

Commits
-------

cd682f5f Changing the declaration of twig.form.render to ensure it won't choke if CsrfServiceProvider is not used.