New revision API: Do not allow call without paper
New revision API: Do not allow call without paper

Submitting papers is still done through another RH, so the API one
does not need to handle it (and would have failed when attempted to do
it anyway)

indico/indico,pferreir/indico,pferreir/indico,DirkHoffmann/indico,ThiefMaster/indico,ThiefMaster/indico,ThiefMaster/indico,indico/indico,DirkHoffmann/indico,indico/indico,ThiefMaster/indico,DirkHoffmann/indico,pferreir/indico,indico/indico,DirkHoffmann/indico,pferreir/indico