Fix error caused by deleted contribs in author list
Fix error caused by deleted contribs in author list

Simply skip deleted contributions and authors who have only deleted
contributions (i.e. with no conference assigned)

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