Update UserAclVoter to determine if user is logged in before checking if they are a super admin

FatalErrorException: Error: Call to a member function isSuperAdmin() on a non-object in vendor/sonata-project/user-bundle/Sonata/UserBundle/Security/Authorization/Voter/UserAclVoter.php line 39
Merge pull request #245 from wcluijt/patch-1

Update UserAclVoter to determine if user is logged in before checking if...