Fix present_notify to return right away when querying current or past msc.

When the target msc is past or is the current one, we want to get immediate
feedback. This patch fixes this behaviour.

Signed-off-by: Axel Davy <axel.davy@ens.fr>
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Keith Packard <keithp@keithp.com>
(cherry picked from commit 882f2d10d99a04a96afc0ce0c8937e16bec3afb5)
Signed-off-by: Julien Cristau <jcristau@debian.org>