Issue #2582295: Fix confirmation cancel links when installed in a subdirectory

Issue #2582295 by julia.klimovsky, seanB, gaurav_manerkar, ranjith_kumar_k_u, Gauravvvv, tim.plunkett, pwolanin, u7aro, SenthilMohith: Fix confirmation cancel links when installed in a subdirectory

Closes #2582295

core/lib/Drupal/Core/Form/ConfirmFormHelper.php

@@ -31,6 +31,10 @@ public static function buildCancelLink(ConfirmFormInterface $form, Request $requ
       $options = UrlHelper::parse($query->get('destination'));
       // @todo Revisit this in https://www.drupal.org/node/2418219.
       try {
+        $base_path = $request->getBasePath();
+        if ($base_path && strpos($options['path'], $base_path) === 0) {
+          $options['path'] = substr($options['path'], mb_strlen($base_path));
+        }
         $url = Url::fromUserInput('/' . ltrim($options['path'], '/'), $options);
       }
       catch (\InvalidArgumentException $e) {