fix js fail in media player

apps/media/js/collection.js

@@ -112,6 +112,7 @@ Collection={
 							Collection.parent.find('tr').removeClass('active');
 							$('tr[data-artist="'+artist.name+'"]').addClass('active');
 						});
+						expander='';
 						if(artist.songs.length>1){
 							expander=$('<a class="expander">&gt;</a>');
 							expander.data('expanded',false);