node: Ensure that processEvents blocks only if there are active events

Active events include:
- expressed Interests and awaiting for Data or Timeout
- set Interest filter

Change-Id: I75631ffca888a66ac7f31f38c7aa5fe204e2d510
diff --git a/include/ndn-cpp/node.hpp b/include/ndn-cpp/node.hpp
index b785be4..b28e91d 100644
--- a/include/ndn-cpp/node.hpp
+++ b/include/ndn-cpp/node.hpp
@@ -317,6 +317,7 @@
 private:
   ptr_lib::shared_ptr<boost::asio::io_service> ioService_;
   ptr_lib::shared_ptr<boost::asio::deadline_timer> pitTimeoutCheckTimer_;
+  bool pitTimeoutCheckTimerActive_;
   ptr_lib::shared_ptr<boost::asio::deadline_timer> processEventsTimeoutTimer_;
   
   ptr_lib::shared_ptr<Transport> transport_;