Fix email sending on registration crash (#1454)

BTCPayServer/Controllers/AccountController.cs

@@ -463,7 +463,7 @@ namespace BTCPayServer.Controllers
 
                     _eventAggregator.Publish(new UserRegisteredEvent()
                     {
-                        Request = Request,
+                        RequestUri = Request.GetAbsoluteRootUri(),
                         User = user,
                         Admin = RegisteredAdmin
                     });