Issue with error checking on Win32 platform fixed

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

src/thread.cpp

@@ -48,7 +48,7 @@ void zmq::thread_t::stop ()
     DWORD rc = WaitForSingleObject (descriptor, INFINITE);
     win_assert (rc != WAIT_FAILED);
     BOOL rc2 = CloseHandle (descriptor);
-    win_assert (rc != 0);
+    win_assert (rc2 != 0);
 }
 
 #else