Fix error after uploading multiple attachments
Fix error after uploading multiple attachments

success is triggered for each file, so we need to use successmultiple
which is called only once.

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