Fixed: Faster artist endpoint (#874)

* Fixed: Speed up AllArtist API endpoint

* New: Display UI before artists have loaded

* Add test of new repository methods

frontend/src/Wanted/CutoffUnmet/CutoffUnmetRow.js

@@ -26,6 +26,10 @@ function CutoffUnmetRow(props) {
     onSelectedChange
   } = props;
 
+  if (!artist) {
+    return null;
+  }
+
   return (
     <TableRow>
       <TableSelectCell