Only change the libraries value in ajax page state if uncompress does not return false.

Closes #3411056

src/StackMiddleware/AjaxPageState.php

@@ -50,7 +50,10 @@ class AjaxPageState implements HttpKernelInterface {
    *   The decompressed ajax_preview_page_state array.
    */
   private function parseAjaxPageState(array $ajax_page_state): array {
-    $ajax_page_state['libraries'] = UrlHelper::uncompressQueryParameter($ajax_page_state['libraries']);
+    $uncompressed = UrlHelper::uncompressQueryParameter($ajax_page_state['libraries']);
+    if ($uncompressed !== FALSE) {
+      $ajax_page_state['libraries'] = $uncompressed;
+    }
     return $ajax_page_state;
   }