minor #62110 [Messenger] Simplify code (HypeMC)

This PR was merged into the 7.4 branch.

Discussion
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[Messenger] Simplify code

| Q             | A
| ------------- | ---
| Branch?       | 7.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        | -
| License       | MIT

Noticed while working on #61843.

There's no reason for the event to be dispatched inside the loop anymore:

1. The event was [originally dispatched outside the loop](#30650).
2. It was later [moved inside the loop](#30676) because of the retry mechanism.
3. [The retry mechanism was later extracted](#34185), so there's no longer a need for the event to be dispatched inside the loop.

Commits
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beeb4b9 [Messenger] Simplify code

Author: nicolas-grekas

src/Symfony/Component/Messenger/Event/SendMessageToTransportsEvent.php

@@ -19,8 +19,8 @@
  *
  * The event is *only* dispatched if the message will actually
  * be sent to at least one transport. If the message is sent
- * to multiple transports, the message is dispatched only once.
- * This message is only dispatched the first time a message
+ * to multiple transports, the event is dispatched only once.
+ * This event is only dispatched the first time a message
  * is sent to a transport, not also if it is retried.
  *
  * @author Ryan Weaver <ryan@symfonycasts.com>

src/Symfony/Component/Messenger/Middleware/SendMessageMiddleware.php

@@ -47,17 +47,16 @@ public function handle(Envelope $envelope, StackInterface $stack): Envelope
             // it's a received message, do not send it back
             $this->logger?->info('Received message {class}', $context);
         } else {
-            $shouldDispatchEvent = true;
             $senders = $this->sendersLocator->getSenders($envelope);
             $senders = \is_array($senders) ? $senders : iterator_to_array($senders);
-            foreach ($senders as $alias => $sender) {
-                if (null !== $this->eventDispatcher && $shouldDispatchEvent) {
-                    $event = new SendMessageToTransportsEvent($envelope, $senders);
-                    $this->eventDispatcher->dispatch($event);
-                    $envelope = $event->getEnvelope();
-                    $shouldDispatchEvent = false;
-                }
 
+            if (null !== $this->eventDispatcher && $senders) {
+                $event = new SendMessageToTransportsEvent($envelope, $senders);
+                $this->eventDispatcher->dispatch($event);
+                $envelope = $event->getEnvelope();
+            }
+
+            foreach ($senders as $alias => $sender) {
                 $this->logger?->info('Sending message {class} with {alias} sender using {sender}', $context + ['alias' => $alias, 'sender' => $sender::class]);
                 $envelope = $sender->send($envelope->with(new SentStamp($sender::class, \is_string($alias) ? $alias : null)));
             }