[ftp] Terminate processing after receiving an error

When an error reply (not 1xx, 2xx or 3xx) was received, ftp_reply()
invoked ftp_done() to close connections, but did not return, and the
rest of code in this function could try to send commands to the closed
control connection.

Signed-off-by: Sergey Vlasov <vsu@altlinux.ru>

src/net/tcp/ftp.c

 		 ( ( status_major == '3' ) && ( ftp->state == FTP_USER ) ) ) ){
 		/* Flag protocol error and close connections */
 		ftp_done ( ftp, -EPROTO );
+		return;
 	}
 
 	/* Open passive connection when we get "PASV" response */