add extra StopAt call to ensure that the simulation ends at some point.

samples/main-ap-wifi.cc

@@ -177,6 +177,8 @@ int main (int argc, char *argv[])
   app->Start (Seconds (0.5));
   app->Stop (Seconds (43.0));
 
+  Simulator::StopAt (Seconds (44.0));
+
   //NodeList::Connect ("/nodes/*/devices/*/*", MakeCallback (&WifiNetDeviceTrace));
   //NodeList::Connect ("/nodes/*/devices/*/phy/state", MakeCallback (&WifiPhyStateTrace));