Could not use Model_User::checkPermission() due to a typo

There was a typo in the function name and the way it was called as well. Usually permissions are checked through `\Nos\User\Permission`.
However this class works only if the user is logged in the admin.

Any application using Model_User as front-end user model would not be able to use `\Nos\User\Permission` and would have to rely on this buggy method call.