fetchart: Improve validation of image dimensions
fetchart: Improve validation of image dimensions

This avoids images being resized unnecessarily if the dimensions
are correct.

diego-plan9/beets,madmouser1/beets,kelvinhammond/beets,diego-plan9/beets,kelvinhammond/beets,parapente/beets,kareemallen/beets,beetbox/beets,jmwatte/beets,mosesfistos1/beetbox,jcoady9/beets,Freso/beets,madmouser1/beets,mried/beets,ibmibmibm/beets,beetbox/beets,artemutin/beets,jmwatte/beets,shamangeorge/beets,swt30/beets,mried/beets,ibmibmibm/beets,beetbox/beets,LordSputnik/beets,m-urban/beets,swt30/beets,pkess/beets,shamangeorge/beets,swt30/beets,jcoady9/beets,beetbox/beets,shamangeorge/beets,ibmibmibm/beets,jackwilsdon/beets,MyTunesFreeMusic/privacy-policy,parapente/beets,lengtche/beets,mosesfistos1/beetbox,mosesfistos1/beetbox,parapente/beets,Kraymer/beets,artemutin/beets,lengtche/beets,SusannaMaria/beets,m-urban/beets,swt30/beets,LordSputnik/beets,pkess/beets,xsteadfastx/beets,artemutin/beets,kareemallen/beets,Kraymer/beets,diego-plan9/beets,xsteadfastx/beets,kareemallen/beets,parapente/beets,MyTunesFreeMusic/privacy-policy,mried/beets,sampsyo/beets,mried/beets,Freso/beets,ibmibmibm/beets,sampsyo/beets,jmwatte/beets,pkess/beets,kelvinhammond/beets,m-urban/beets,madmouser1/beets,SusannaMaria/beets,MyTunesFreeMusic/privacy-policy,m-urban/beets,LordSputnik/beets,shamangeorge/beets,mosesfistos1/beetbox,artemutin/beets,xsteadfastx/beets,xsteadfastx/beets,Kraymer/beets,jackwilsdon/beets,lengtche/beets,jackwilsdon/beets,jcoady9/beets,kelvinhammond/beets,Freso/beets,jmwatte/beets,pkess/beets,SusannaMaria/beets,jackwilsdon/beets,lengtche/beets,Freso/beets,Kraymer/beets,MyTunesFreeMusic/privacy-policy,LordSputnik/beets,diego-plan9/beets,sampsyo/beets,madmouser1/beets,kareemallen/beets,SusannaMaria/beets,sampsyo/beets,jcoady9/beets