Possible blocking on waitCh

```
func onError() {
    ...
    e.waitCh <- &drivers.ExitResult
}
```

waitCh is defined as
```
func newDtleTaskHandle() {
		waitCh:      make(chan *drivers.ExitResult, 1),
}
```

and read only once
```
func handleWait() {
	case result := <-handle.waitCh:
}
```

A concurrent call to `onError` might block on waitCh forever.