idle.screensaver / idle.lock of 0 was included in Math.min(), so
IdleMonitor's timeout became 0. Releasing a Wayland idle inhibitor
(SDL's default screensaver inhibit) then reported idle immediately and
locked the session even when lock had been "disabled" by setting it to 0.
Treat 0 as disabled when computing the first idle deadline, do not start
the corresponding action, and leave IdleMonitor off when both timeouts
are 0.
Fixes#10860
Paulo Geyer
14921a956e