Fix bad redirection to login page for anonymous blob download

1. setup shibboleth server allowing anonymous configuration
2. setup Nuxeo server with anonymous login enabled
3. log in
4. create a File document with a file attached
5. copy in a text editor the document link
6. copy in a text editor the document blob link
7. log out
8. attempt to access the document link -> Nuxeo redirects to the IdP login page
9. attempt to access the blob link -> Nuxeo does not redirect and gives a forbidden response:

   You don't have the necessary permission to do the requested action.
   
   You don't have sufficient rights to perform this operation.

This does not happen to versions earlier than 7.10