Payment channels: invoke destroyConn on server side even when client requested it.

This allows servers to do something useful when the channel closes normally, like forward the money onwards.

core/src/main/java/com/google/bitcoin/protocols/channels/PaymentChannelServer.java

@@ -433,6 +433,7 @@ public class PaymentChannelServer {
                     log.info("Sending CLOSE back without broadcast settlement tx.");
                 }
                 conn.sendToClient(msg.build());
+                conn.destroyConnection(clientRequestedClose);
             }
 
             @Override