Throw an error if IndividualResource cannot be rendered

With the current code, this condition will always fail. Prevent this
from silently passing and instead raise an error.

static-site/src/components/ListResources/IndividualResource.tsx

@@ -133,10 +133,11 @@ export const IndividualResource = ({
   const ref = useRef<HTMLDivElement>(null);
   const [topOfColumn, setTopOfColumn] = useState(false);
   useEffect(() => {
-    // don't do anything if the ref is undefined or the parent is not a div (IndividualResourceContainer)
-    if (!ref.current
-     || !ref.current.parentNode
-     || ref.current.parentNode.nodeName != 'DIV') return;
+    if (ref.current === null ||
+        ref.current.parentNode === null ||
+        ref.current.parentNode.nodeName != 'DIV') {
+      throw new InternalError("ref must be defined and the parent must be a div (IndividualResourceContainer).");
+     }
 
     /* The column CSS is great but doesn't allow us to know if an element is at
     the top of its column, so we resort to JS */