syslet engine: residual fix

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/engines/syslet-rw.c b/engines/syslet-rw.c
index 40298cb..fe400da 100644
--- a/engines/syslet-rw.c
+++ b/engines/syslet-rw.c
@@ -46,7 +46,7 @@
 
 		io_u = atom->private;
 		ret = *atom->ret_ptr;
-		if (ret > 0)
+		if (ret >= 0)
 			io_u->resid = io_u->xfer_buflen - ret;
 		else if (ret < 0)
 			io_u->error = ret;