making sure sentinel is rendered even when empty

for cases like Listbox in Combobox, the content area is actually 0 since we dont have a height on the listbox nor does it reserve room like table layout

Author: LFDanLu

packages/react-aria-components/src/Virtualizer.tsx

@@ -102,7 +102,9 @@ function CollectionRoot({collection, persistedKeys, scrollRef, renderDropIndicat
     onScrollEnd: state.endScrolling
   }, scrollRef!);
 
-  if (state.contentSize.area === 0) {
+  // TODO: wull have to update this when multi section loading is implemented, will need to check if all items in a collection are loaders instead perhaps
+  let hasLoadingSentinel = collection.size === 1 && collection.getItem(collection.getFirstKey()!)!.type === 'loader';
+  if (state.contentSize.area === 0 && !hasLoadingSentinel) {
     return null;
   }