java.lang.NullPointerException: Attempt to read from field 'int vn.hunghd.flutterdownloader.DownloadTask.status' on a null object reference

Exception on flutter_downloader version 1.7.2

```
Fatal Exception: java.lang.NullPointerException: Attempt to read from field 'int vn.hunghd.flutterdownloader.DownloadTask.status' on a null object reference
at vn.hunghd.flutterdownloader.DownloadWorker.onStopped(DownloadWorker.java:178)
at androidx.work.ListenableWorker.stop(ListenableWorker.java:283)
at androidx.work.impl.workers.ConstraintTrackingWorker.onStopped(ConstraintTrackingWorker.java:181)
at androidx.work.ListenableWorker.stop(ListenableWorker.java:283)
at androidx.work.impl.WorkerWrapper.interrupt(WorkerWrapper.java:397)
at androidx.work.impl.Processor.interrupt(Processor.java:340)
at androidx.work.impl.Processor.stopWork(Processor.java:190)
at androidx.work.impl.utils.StopWorkRunnable.run(StopWorkRunnable.java:73)
at androidx.work.impl.utils.SerialExecutor$Task.run(SerialExecutor.java:91)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
at java.lang.Thread.run(Thread.java:762)
```