minor #17763 Remove unnecessary retrieval and setting of data (Trent …

…Steel)

This PR was submitted for the 2.8 branch but it was merged into the 2.3 branch instead (closes #17763).

Discussion
----------

Remove unnecessary retrieval and setting of data

| Q             | A
| ------------- | ---
| Bug fix?      | No
| New feature?  | No - optimisation
| BC breaks?    | No
| Deprecations? | No
| Tests pass?   | Yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | None

Commits
-------

ea52400 remove unnecessary retrieval and setting of data

src/Symfony/Component/Form/Extension/Csrf/EventListener/CsrfValidationListener.php

@@ -84,9 +84,10 @@ public function __construct($fieldName, CsrfProviderInterface $csrfProvider, $in
     public function preSubmit(FormEvent $event)
     {
         $form = $event->getForm();
-        $data = $event->getData();
 
         if ($form->isRoot() && $form->getConfig()->getOption('compound')) {
+            $data = $event->getData();
+
             if (!isset($data[$this->fieldName]) || !$this->csrfProvider->isCsrfTokenValid($this->intention, $data[$this->fieldName])) {
                 $errorMessage = $this->errorMessage;
 
@@ -99,10 +100,9 @@ public function preSubmit(FormEvent $event)
 
             if (is_array($data)) {
                 unset($data[$this->fieldName]);
+                $event->setData($data);
             }
         }
-
-        $event->setData($data);
     }
 
     /**