AudioAddict: fix artist name retrieval
AudioAddict: fix artist name retrieval

Sometimes, the artist field is empty
It is then retrieved from the track field

RouxRC/weboob,nojhan/weboob-devel,nojhan/weboob-devel,laurent-george/weboob,laurent-george/weboob,laurent-george/weboob,frankrousseau/weboob,Konubinix/weboob,Konubinix/weboob,nojhan/weboob-devel,Boussadia/weboob,willprice/weboob,yannrouillard/weboob,yannrouillard/weboob,willprice/weboob,RouxRC/weboob,frankrousseau/weboob,Boussadia/weboob,RouxRC/weboob,Konubinix/weboob,Boussadia/weboob,sputnick-dev/weboob,sputnick-dev/weboob,Boussadia/weboob,yannrouillard/weboob,willprice/weboob,sputnick-dev/weboob,frankrousseau/weboob