ensure legacy event dispatcher compatibility

Author: xabbuh

Transport/AbstractTransport.php

@@ -14,6 +14,7 @@
 use Psr\Log\LoggerInterface;
 use Psr\Log\NullLogger;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
+use Symfony\Component\EventDispatcher\LegacyEventDispatcherProxy;
 use Symfony\Component\Mailer\DelayedSmtpEnvelope;
 use Symfony\Component\Mailer\Event\MessageEvent;
 use Symfony\Component\Mailer\Exception\TransportException;
@@ -36,7 +37,7 @@ abstract class AbstractTransport implements TransportInterface
 
     public function __construct(EventDispatcherInterface $dispatcher = null, LoggerInterface $logger = null)
     {
-        $this->dispatcher = $dispatcher;
+        $this->dispatcher = LegacyEventDispatcherProxy::decorate($dispatcher);
         $this->logger = $logger ?: new NullLogger();
     }