helper: Fix NDN stack initialization when using VisualSimulatorImpl

Change-Id: Ide284d87a0d06c11a7191fdea5b58169392281a2
diff --git a/helper/ndn-strategy-choice-helper.cpp b/helper/ndn-strategy-choice-helper.cpp
index 215d34b..43cd9fd 100644
--- a/helper/ndn-strategy-choice-helper.cpp
+++ b/helper/ndn-strategy-choice-helper.cpp
@@ -64,8 +64,7 @@
 
   Simulator::ScheduleWithContext(node->GetId(), Seconds(0),
                                  &StrategyChoiceHelper::sendCommand, parameters, node);
-  Simulator::Stop(Seconds(0));
-  Simulator::Run();
+  StackHelper::ProcessWarmupEvents();
 }
 
 void