cfg: When send_shutdown fails, clear shutdown_con

When (for example) CS_ERR_TRY_AGAIN is returned, shutdown_con was still
set resulting in following situation:
- It was not possible to call shutdown again
- Shutdown didn't proceed

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Fabio M. Di Nitto <fdinitto@redhat.com>

services/cfg.c

@@ -971,6 +971,7 @@ static void message_handler_req_lib_cfg_tryshutdown (
 		result = send_shutdown();
 		if (result == -1) {
 			error = CS_ERR_TRY_AGAIN;
+			shutdown_con = NULL;
 		}
 
 		res_lib_cfg_tryshutdown.header.size = sizeof(struct res_lib_cfg_tryshutdown);