security: Double-check that component/block name in AJAX call is a string

Author: jissereitsma

Controller/Index/Html.php

@@ -111,7 +111,7 @@ private function getComponentUpdates(array $updates, LayoutInterface $layout): a
     {
         $componentUpdates = [];
         foreach ($updates as $updateIndex => $update) {
-            if (!isset($update['blockName'])) {
+            if (!isset($update['blockName']) || !is_string($update['blockName'])) {
                 continue;
             }