[ndnSIM] Add lost scheduler code

This commit to be merged with scheduler fix in the next rebase cycle

Change-Id: I31580a9d15fab10a5ca53a110dd71ae5f984a608
diff --git a/ndn-cxx/util/scheduler.cpp b/ndn-cxx/util/scheduler.cpp
index 6d9b766..8dff072 100644
--- a/ndn-cxx/util/scheduler.cpp
+++ b/ndn-cxx/util/scheduler.cpp
@@ -124,7 +124,9 @@
 
   if (info->queueIt == m_queue.begin()) {
     if (m_timerEvent) {
-      ns3::Simulator::Remove(*m_timerEvent);
+      if (!m_timerEvent->IsExpired()) {
+        ns3::Simulator::Remove(*m_timerEvent);
+      }
       m_timerEvent.reset();
     }
   }
@@ -140,7 +142,9 @@
 {
   m_queue.clear();
   if (m_timerEvent) {
-    ns3::Simulator::Remove(*m_timerEvent);
+    if (!m_timerEvent->IsExpired()) {
+      ns3::Simulator::Remove(*m_timerEvent);
+    }
     m_timerEvent.reset();
   }
 }