[MIN] Improve add material -> other material type
[MIN] Improve add material -> other material type

- Display a meaningful message instead of nothing if no
  material type name has been entered.
- fixes #480

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