Respond to DYNVC_CLOSE like described in MS-RDPEDYC

Fix bug for issue https://github.com/FreeRDP/FreeRDP/issues/1375

When the DVC server manager initiates closing a channel, it sends a Close Request PDU that specifies the ChannelId to the DVC client manager. The client responds with a Close Response PDU that specifies the ChannelId.

The client response was missing.