alarm_manager: prevent stale idle() timers
alarm_manager: prevent stale idle() timers

rgov/mopidy-alarmclock,rgov/mopidy-alarmclock,DavisNT/mopidy-alarmclock,DavisNT/mopidy-alarmclock,rgov/mopidy-alarmclock,DavisNT/mopidy-alarmclock,michaellunzer/mopidy-alarmclock,michaellunzer/mopidy-alarmclock,michaellunzer/mopidy-alarmclock