fix: allow dismissing an alarm that was deleted while ringing

[MiMoHo]

Type of change(s)

• Bug fix

What changed and why

AlarmService.onStartCommand looked up the alarm in the database up front and, whenever the record was missing, bailed out via stopSelfIfIdle() and returned START_NOT_STICKY. When an alarm is deleted while it is ringing (AlarmsAdapter.deleteItems() calls dbHelper.deleteAlarms(...) and posts AlarmEvent.Refresh but never stops the service), that lookup returns null. Every dismiss / snooze / silence path funnels through AlarmController -> ACTION_STOP_ALARM -> onStartCommand, so the null guard swallowed the stop request: stopActiveAlarm(alarmId) was never reached and stopSelfIfIdle() did nothing because activeAlarm was still set. The result was an alarm that keeps sounding with no way to dismiss or snooze it.

Only the START path actually needs the alarm object; the STOP path merely compares the id against the currently active alarm. This moves the DB lookup and its null guard into the ACTION_START_ALARM branch, leaving ACTION_STOP_ALARM able to stop a ringing alarm by id even after its DB row is gone. Behavior for the start path is unchanged.

Tests performed

• detekt, lint, unit tests and the build all pass locally (CI-equivalent).
• Source-verified: AlarmService now null-guards getAlarmWithId(alarmId) inside the ACTION_START_ALARM branch so a still-ringing alarm that was deleted from the DB can be dismissed instead of leaving the service stuck. This is a defensive null check with a clear, contained effect.
• Note: staging a ringing alarm that is then deleted mid-ring is impractical on a stock emulator, so verification is via CI + code review.

Closes the following issue(s)

• Closes Not possible to stop an alarm that was deleted #406

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator (verified via CI + source review; see Tests performed).
• I updated the "Unreleased" section in CHANGELOG.md (if applicable).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• I understand every change in this pull request.

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