startup-notification: Fix timeout computation

Commit f68c04ba "Crash/stack smash on some architectures" had a typo that would mix the values of usecs and secs, causing a very long busy cursor when the startup notification never arrives.

Signed-off-by: Olivier Fourdan fourdan@xfce.org Fixes: f68c04ba - "Crash/stack smash on some architectures" Closes: #518 (closed)