Fix error in roombooking occurrence creation
Fix error in roombooking occurrence creation

This broke with the sqlalchemy update. It might be a bug in sqlalchemy
but 'fetch' evaluation is safer here anyway.

DirkHoffmann/indico,mvidalgarcia/indico,OmeGak/indico,OmeGak/indico,pferreir/indico,mic4ael/indico,ThiefMaster/indico,DirkHoffmann/indico,mvidalgarcia/indico,ThiefMaster/indico,indico/indico,OmeGak/indico,mic4ael/indico,DirkHoffmann/indico,indico/indico,mvidalgarcia/indico,mvidalgarcia/indico,mic4ael/indico,ThiefMaster/indico,indico/indico,indico/indico,OmeGak/indico,pferreir/indico,DirkHoffmann/indico,ThiefMaster/indico,pferreir/indico,mic4ael/indico,pferreir/indico