fix(approval): posts approved for deleted users error

In certain edge cases posts get approved through moderative action and
throws an error when the user has already been deleted.

Ref: DISCUSS-11K on sentry

extensions/approval/src/Listener/ApproveContent.php

@@ -13,7 +13,7 @@ use Flarum\Approval\Event\PostWasApproved;
 use Flarum\Post\Event\Saving;
 use Illuminate\Contracts\Events\Dispatcher;
 
-class ApproveContent
+class   ApproveContent
 {
     /**
      * @param Dispatcher $events
@@ -69,7 +69,9 @@ class ApproveContent
 
         $discussion->save();
 
-        $user->refreshCommentCount();
-        $user->save();
+        if ($discussion->user) {
+            $user->refreshCommentCount();
+            $user->save();
+        }
     }
 }