Avoid leaving the event stack in a dirty state if an event listener throws, fixes #9846

src/Composer/EventDispatcher/EventDispatcher.php

@@ -157,6 +157,7 @@ class EventDispatcher
 
         $this->pushEvent($event);
 
+        try {
             $returnMax = 0;
             foreach ($listeners as $callable) {
                 $return = 0;
@@ -294,6 +295,11 @@ class EventDispatcher
                     break;
                 }
             }
+        } catch (\Exception $e) {
+            $this->popEvent();
+
+            throw $e;
+        }
 
         $this->popEvent();