bug #29822 [EventDispatcher] Fix unknown priority (ro0NL)

This PR was merged into the 3.4 branch.

Discussion
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[EventDispatcher] Fix unknown priority

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | #...   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->

Somehow, after #29411 the profiler actually shows the security firewall `ContextListener`.

This listener removes itself at call time, but at this point it's wrapped reference is already in the call stack; to be displayed in the profiler.

Because the wrapped listener lazily collects its priority - it asks it from the dispatcher -  we get null; the listener was already removed.

This causes the profiler to render `-` by default:

![image](https://user-images.githubusercontent.com/1047696/50850320-d5c5ee80-1379-11e9-8516-0c6bc54512ce.png)

This fixes it by always passing the expected priority at call time.

Commits
-------

9fb619a [EventDispatcher] Fix unknown priority

src/Symfony/Component/EventDispatcher/Debug/WrappedListener.php

@@ -29,6 +29,7 @@ class WrappedListener
     private $dispatcher;
     private $pretty;
     private $stub;
+    private $priority;
     private static $hasClassStub;
 
     public function __construct($listener, $name, Stopwatch $stopwatch, EventDispatcherInterface $dispatcher = null)
@@ -96,19 +97,22 @@ public function getInfo($eventName)
 
         return [
             'event' => $eventName,
-            'priority' => null !== $this->dispatcher ? $this->dispatcher->getListenerPriority($eventName, $this->listener) : null,
+            'priority' => null !== $this->priority ? $this->priority : (null !== $this->dispatcher ? $this->dispatcher->getListenerPriority($eventName, $this->listener) : null),
             'pretty' => $this->pretty,
             'stub' => $this->stub,
         ];
     }
 
     public function __invoke(Event $event, $eventName, EventDispatcherInterface $dispatcher)
     {
+        $dispatcher = $this->dispatcher ?: $dispatcher;
+
         $this->called = true;
+        $this->priority = $dispatcher->getListenerPriority($eventName, $this->listener);
 
         $e = $this->stopwatch->start($this->name, 'event_listener');
 
-        \call_user_func($this->listener, $event, $eventName, $this->dispatcher ?: $dispatcher);
+        \call_user_func($this->listener, $event, $eventName, $dispatcher);
 
         if ($e->isStarted()) {
             $e->stop();