[grooveshark] fix bug : no more field AvgRate
[grooveshark] fix bug : no more field AvgRate

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