minor #9929 Fixed security expression testing user (HeahDude)

This PR was submitted for the master branch but it was merged into the 2.8 branch instead (closes #9929).

Discussion
----------

Fixed security expression testing user

The example "user and ..." is broken when the user is a string.

Commits
-------

bdd20d3 Fixed security expression testing user

Author: javiereguiluz

security.rst

@@ -964,15 +964,15 @@ You can also use expressions inside your templates:
     .. code-block:: html+jinja
 
         {% if is_granted(expression(
-            '"ROLE_ADMIN" in roles or (user and user.isSuperAdmin())'
+            '"ROLE_ADMIN" in roles or (not is_anonymous() and user.isSuperAdmin())'
         )) %}
             <a href="...">Delete</a>
         {% endif %}
 
     .. code-block:: html+php
 
         <?php if ($view['security']->isGranted(new Expression(
-            '"ROLE_ADMIN" in roles or (user and user.isSuperAdmin())'
+            '"ROLE_ADMIN" in roles or (not is_anonymous() and user.isSuperAdmin())'
         ))): ?>
             <a href="...">Delete</a>
         <?php endif; ?>

security/expressions.rst

@@ -18,7 +18,7 @@ accepts an :class:`Symfony\\Component\\ExpressionLanguage\\Expression` object::
     public function indexAction()
     {
         $this->denyAccessUnlessGranted(new Expression(
-            '"ROLE_ADMIN" in roles or (user and user.isSuperAdmin())'
+            '"ROLE_ADMIN" in roles or (not is_anonymous() and user.isSuperAdmin())'
         ));
 
         // ...