Added exception when setAutoInitialize is called when locked

src/Symfony/Component/Form/FormConfigBuilder.php

@@ -855,6 +855,10 @@ class FormConfigBuilder implements FormConfigBuilderInterface
      */
     public function setAutoInitialize($initialize)
     {
+        if ($this->locked) {
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
+        }
+
         $this->autoInitialize = (bool) $initialize;
 
         return $this;