Don't try and close the pipe to the grandparent if it has already been closed

(i.e. we have restarted Xend).

Signed-off-by: Ewan Mellor <ewan@xensource.com>

tools/python/xen/xend/server/SrvDaemon.py

@@ -167,8 +167,9 @@ class Daemon:
             while True:
                 pid = self.fork_pid()
                 if pid:
-                    os.close(w)
-                    w = False
+                    if w is not None:
+                        os.close(w)
+                        w = None
 
                     (_, status) = os.waitpid(pid, 0)