Fix unnecessary error popup during shutdown if the wireless device driver is running and mdns de-registration fails. Fixes #1262819 [Calibre throws error when stopping wireless device connection](https://bugs.launchpad.net/calibre/+bug/1262819)

Merge branch 'master' of https://github.com/cbhaley/calibre

src/calibre/devices/smart_device_app/driver.py

@@ -1571,8 +1571,12 @@ class SMART_DEVICE_APP(DeviceConfig, DevicePlugin):
     def shutdown(self):
         if getattr(self, 'listen_socket', None) is not None:
             self.connection_listener.stop()
+            try:
                 unpublish_zeroconf('calibre smart device client',
                                    '_calibresmartdeviceapp._tcp', self.port, {})
+            except:
+                self._debug('deregistration with bonjour failed')
+                traceback.print_exc()
             self._close_listen_socket()
 
     # Methods for dynamic control