is_secure is not checked before generating cached files

[tdmedia]

Scenario:

1. Form class makes reference to sfGuardUser like so:

$user = sfContext::getInstance()->getUser();
...
if ($schoolId = $user->getGuardUser()->getProfile()->getSchoolId())

1. The security.yml file for the module is set as follows:

all:
is_secure: true

1. Clear the symfony cache.
2. User is logged out and tries to go the module.

Expected result: User is redirected to a login page.

Actual result: 500 error

Fatal error: Call to a member function getProfile() on a non-object in /web/edits_net/editsapp/lib/form/doctrine/sfGuardUserProfileForm.class.php on line 29

If the module is visited once by an authenticated user after the cache is cleared, then subsequent visits by unauthenticated users don't have the problem. Adding a check for isAuthenticated() in the form class prevents the problem.