bug #32331 [Workflow] only decorate when an event dispatcher was pass…

…ed (xabbuh)

This PR was merged into the 4.3 branch.

Discussion
----------

[Workflow] only decorate when an event dispatcher was passed

| Q             | A
| ------------- | ---
| Branch?       | 4.3
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #32330
| License       | MIT
| Doc PR        |

Commits
-------

f19f28a only decorate when an event dispatcher was passed

src/Symfony/Component/Workflow/Workflow.php

@@ -43,7 +43,7 @@ public function __construct(Definition $definition, MarkingStoreInterface $marki
     {
         $this->definition = $definition;
         $this->markingStore = $markingStore ?: new MultipleStateMarkingStore();
-        $this->dispatcher = LegacyEventDispatcherProxy::decorate($dispatcher);
+        $this->dispatcher = null !== $dispatcher ? LegacyEventDispatcherProxy::decorate($dispatcher) : null;
         $this->name = $name;
     }