Fix triggering onStopped and onEnded when restarting a stopped timer

[aemelyanovff]

Calling onResetTimer on a stopped timer triggers onStop and onEnded events. I expect these event not to trigger if the timer is not running.

Consider this use case. I want to create a countdown timer that restarts from the beginning every 5 seconds:

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {

  final StopWatchTimer _stopWatchTimer = StopWatchTimer(
    mode: StopWatchMode.countDown,
    presetMillisecond: 5000,
  );

  @override
  void initState() {
    super.initState();
    _stopWatchTimer.fetchEnded.listen((v) {
      print('Ended, value: $v');
      _stopWatchTimer.onResetTimer();
      _stopWatchTimer.onStartTimer();
    });
    _stopWatchTimer.onStartTimer();
  }

  @override
  void dispose() async {
    super.dispose();
    await _stopWatchTimer.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Container();
  }
}

I expect this code to work, but every time in calls onResetTimer it also triggers fetchEnded, so it enters an infinite loop.

This fix replaces isRunning || _startTime > 0 with isRunning && _startTime > 0, so now resetting a stopped container doesn't trigger these events.

[hukusuke1007]

Thank you!