Fixed #12462 - Fixed edge case with auth backends that don't support object...

Fixed #12462 - Fixed edge case with auth backends that don't support object permissions. Thanks to Florian Apolloner for catching it.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12032 bcc190cf-cafb-0310-a4f2-bffc1f526a37