MT#63171 StatsUDPServer: use correct FD flag

Zero is a valid file descriptor. Use -1 as flag.

Change-Id: I9347e38ea51d0e9274941e8e888432b990f55c5a
(cherry picked from commit e684718807)
(cherry picked from commit 5adfed016d)

core/plug-in/stats/StatsUDPServer.cpp

@@ -114,14 +114,14 @@ StatsUDPServer* StatsUDPServer::instance()
 }
 
 StatsUDPServer::StatsUDPServer()
-  : sd(0)
+  : sd(-1)
 {
   sc = AmSessionContainer::instance();
 }
 
 StatsUDPServer::~StatsUDPServer()
 {
-  if(sd)
+  if (sd != -1)
     close(sd);
 }