embedart: try extracting from items until success
embedart: try extracting from items until success

Don't stop at the first item but try them all.
Fix #1261

dfc/beets,arabenjamin/beets,mathstuf/beets,jackwilsdon/beets,randybias/beets,drm00/beets,randybias/beets,randybias/beets,marcuskrahl/beets,PierreRust/beets,MyTunesFreeMusic/privacy-policy,marcuskrahl/beets,ruippeixotog/beets,lengtche/beets,mathstuf/beets,swt30/beets,Freso/beets,multikatt/beets,beetbox/beets,gabrielaraujof/beets,SusannaMaria/beets,jackwilsdon/beets,ttsda/beets,moodboom/beets,mried/beets,tima/beets,mosesfistos1/beetbox,m-urban/beets,artemutin/beets,gabrielaraujof/beets,Kraymer/beets,asteven/beets,shamangeorge/beets,ttsda/beets,kareemallen/beets,MyTunesFreeMusic/privacy-policy,ibmibmibm/beets,jcoady9/beets,shanemikel/beets,YetAnotherNerd/beets,tima/beets,diego-plan9/beets,ruippeixotog/beets,pkess/beets,Dishwishy/beets,sadatay/beets,mosesfistos1/beetbox,mosesfistos1/beetbox,Andypsamp/CODfinalJUNIT,imsparsh/beets,asteven/beets,madmouser1/beets,swt30/beets,imsparsh/beets,diego-plan9/beets,shanemikel/beets,imsparsh/beets,pkess/beets,artemutin/beets,madmouser1/beets,diego-plan9/beets,Kraymer/beets,Kraymer/beets,beetbox/beets,jmwatte/beets,ttsda/beets,lengtche/beets,kelvinhammond/beets,LordSputnik/beets,LordSputnik/beets,kareemallen/beets,SusannaMaria/beets,drm00/beets,jackwilsdon/beets,Andypsamp/CODjunit,Andypsamp/CODjunit,jmwatte/beets,kelvinhammond/beets,sampsyo/beets,artemutin/beets,jcoady9/beets,xsteadfastx/beets,ruippeixotog/beets,randybias/beets,ibmibmibm/beets,swt30/beets,mried/beets,lengtche/beets,SusannaMaria/beets,SusannaMaria/beets,YetAnotherNerd/beets,ttsda/beets,dfc/beets,untitaker/beets,Kraymer/beets,sampsyo/beets,PierreRust/beets,sadatay/beets,mathstuf/beets,asteven/beets,mathstuf/beets,kareemallen/beets,PierreRust/beets,arabenjamin/beets,shamangeorge/beets,ruippeixotog/beets,mosesfistos1/beetbox,pkess/beets,dfc/beets,asteven/beets,arabenjamin/beets,xsteadfastx/beets,kelvinhammond/beets,Freso/beets,Dishwishy/beets,jcoady9/beets,pkess/beets,untitaker/beets,Freso/beets,kareemallen/beets,MyTunesFreeMusic/privacy-policy,Andypsamp/CODjunit,jcoady9/beets,Andypsamp/CODfinalJUNIT,YetAnotherNerd/beets,kelvinhammond/beets,shanemikel/beets,Dishwishy/beets,sampsyo/beets,beetbox/beets,Andypsamp/CODfinalJUNIT,lightwang1/beets,untitaker/beets,lightwang1/beets,shanemikel/beets,diego-plan9/beets,moodboom/beets,drm00/beets,artemutin/beets,MyTunesFreeMusic/privacy-policy,tima/beets,beetbox/beets,m-urban/beets,untitaker/beets,m-urban/beets,Dishwishy/beets,madmouser1/beets,lightwang1/beets,multikatt/beets,dfc/beets,swt30/beets,madmouser1/beets,parapente/beets,multikatt/beets,drm00/beets,LordSputnik/beets,xsteadfastx/beets,jmwatte/beets,ibmibmibm/beets,jmwatte/beets,xsteadfastx/beets,imsparsh/beets,marcuskrahl/beets,Andypsamp/CODjunit,jackwilsdon/beets,Freso/beets,mried/beets,LordSputnik/beets,arabenjamin/beets,parapente/beets,sadatay/beets,lengtche/beets,Andypsamp/CODfinalJUNIT,YetAnotherNerd/beets,sadatay/beets,shamangeorge/beets,shamangeorge/beets,mried/beets,PierreRust/beets,Andypsamp/CODfinalJUNIT,multikatt/beets,parapente/beets,lightwang1/beets,marcuskrahl/beets,gabrielaraujof/beets,moodboom/beets,moodboom/beets,gabrielaraujof/beets,Andypsamp/CODjunit,tima/beets,sampsyo/beets,parapente/beets,m-urban/beets,ibmibmibm/beets