client: stop leaking "keep-alive" go-routine

When keep-alive is enabled, Client.loop() creates a go-routine to
provide the functionality, however, the go-routine never exits, not even
when the client's SSH connection to the server has been torn down, thus
leaking the go-routine.

This typically isn't a problem for the command-line chisel client since
it is single-use; the SSH connection is torn down only when the client
is terminating anyway. However, such a go-routine leak could become
problematic if the client ever learns to manage multiple SSH connections
(perhaps, say, via an interactive mode) or when chisel is used as a
library by some other program which manages multiple connections.
Therefore, ensure that the go-routine terminates when the SSH connection
is torn down.

Author: sunshineco

client/client.go

@@ -149,6 +149,8 @@ func (c *Client) loop() {
 			for range time.Tick(c.config.KeepAlive) {
 				if c.sshConn != nil {
 					c.sshConn.SendRequest("ping", true, nil)
+				} else {
+					break
 				}
 			}
 		}()