The Scoping-element should be added as soom as we want to include
RequesterID, IDPList or ProxyCount in the message. We must therefore
add it even if IDPList isn't specified.

Thanks to Lucas van Lierop for finding this bug!

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@3265 44740490-163a-0410-bde0-09ae8108e29a