Add ->done variable to force exit when we know we are done

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.c b/fio.c
index 16e19c8..bc837c4 100644
--- a/fio.c
+++ b/fio.c
@@ -724,6 +724,8 @@
 {
 	unsigned long long io_done;
 
+	if (td->done)
+		return 0;
 	if (td->o.time_based)
 		return 1;
 	if (td->o.loops) {