B2B-2464: Improve category children loading

Author: rganin

app/code/Magento/CatalogGraphQl/Model/Category/CategoryFilter.php

@@ -85,7 +85,7 @@ public function getResult(array $criteria, StoreInterface $store, array $attribu
                 'e.entity_id'
             );
 
-        $categoryIds = $collection->getLoadedIds();
+        $categoryIds = $collection->load()->getLoadedIds();
 
         $totalPages = 0;
         if ($collection->getSize() > 0 && $searchCriteria->getPageSize() > 0) {