[EventDispatcher] removed unneeded code

src/Symfony/Component/EventDispatcher/EventDispatcher.php

@@ -94,13 +94,6 @@ class EventDispatcher implements EventDispatcherInterface
      */
     public function addListener($eventName, $listener, $priority = 0)
     {
-        if (!isset($this->listeners[$eventName][$priority])) {
-            if (!isset($this->listeners[$eventName])) {
-                $this->listeners[$eventName] = array();
-            }
-            $this->listeners[$eventName][$priority] = array();
-        }
-
         $this->listeners[$eventName][$priority][] = $listener;
     }