B2B-2469: Improve category children loading

- review changes

Author: rganin

dev/tests/api-functional/testsuite/Magento/GraphQl/Catalog/CategoryListTest.php

@@ -1009,6 +1009,7 @@ public function testCategoryListPaginationLimitsNotAppliedToChildren()
         $response = $this->graphQlQuery($this->getQueryForPage(1));
         $this->assertArrayNotHasKey('errors', $response);
         $this->assertArrayHasKey('categoryList', $response);
+        $this->assertCount(1, $response['categoryList']);
         $baseCategory = $response['categoryList'][0];
         $this->assertEquals('Category 1', $baseCategory['name']);
         $this->assertCount(2, $baseCategory['children']);
@@ -1019,13 +1020,15 @@ public function testCategoryListPaginationLimitsNotAppliedToChildren()
         $response = $this->graphQlQuery($this->getQueryForPage(2));
         $this->assertArrayNotHasKey('errors', $response);
         $this->assertArrayHasKey('categoryList', $response);
+        $this->assertCount(1, $response['categoryList']);
         $baseCategory = $response['categoryList'][0];
         $this->assertEquals('Category 2', $baseCategory['name']);
         $this->assertCount(0, $baseCategory['children']);
 
         $response = $this->graphQlQuery($this->getQueryForPage(3));
         $this->assertArrayNotHasKey('errors', $response);
         $this->assertArrayHasKey('categoryList', $response);
+        $this->assertCount(1, $response['categoryList']);
         $baseCategory = $response['categoryList'][0];
         $this->assertEquals('Movable', $baseCategory['name']);
         $this->assertCount(0, $baseCategory['children']);