client: dec sum_stat_clients if one a client is disconnected

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/client.c b/client.c
index c40511e..31b4862 100644
--- a/client.c
+++ b/client.c
@@ -137,6 +137,7 @@
 
 	free(client);
 	nr_clients--;
+	sum_stat_clients--;
 }
 
 static void __fio_client_add_cmd_option(struct fio_client *client,