[Form] Move check of class existence out of closure

Author: issei-m

src/Symfony/Component/Form/Extension/Core/Type/FileType.php

@@ -92,9 +92,12 @@ public function finishView(FormView $view, FormInterface $form, array $options)
      */
     public function configureOptions(OptionsResolver $resolver)
     {
-        $dataClass = function (Options $options) {
-            return $options['multiple'] || !class_exists('Symfony\Component\HttpFoundation\File\File') ? null : 'Symfony\Component\HttpFoundation\File\File';
-        };
+        $dataClass = null;
+        if (class_exists('Symfony\Component\HttpFoundation\File\File')) {
+            $dataClass = function (Options $options) {
+                return $options['multiple'] ? null : 'Symfony\Component\HttpFoundation\File\File';
+            };
+        }
 
         $emptyData = function (Options $options) {
             return $options['multiple'] ? array() : null;