ZMQII-1: fix for devpoll, kqueue & poll

src/poll.cpp

@@ -52,10 +52,10 @@ zmq::poll_t::poll_t () :
 
 zmq::poll_t::~poll_t ()
 {
+    worker.stop ();
+
     //  Make sure there are no fds registered on shutdown.
     zmq_assert (load.get () == 0);
-
-    worker.stop ();
 }
 
 zmq::handle_t zmq::poll_t::add_fd (fd_t fd_, i_poll_events *events_)