Write error if dupe task scheduled results are received

This shouldn't be required if transactions and q2q transfer work properly, but recently we have seen a couple of instances where the responses have been duped. Need to add tracing if this arises:

```
public void HandleTaskCompletedEvent(TaskCompletedEvent completedEvent)
{
int taskId = completedEvent.TaskScheduledId;
if (openTasks.ContainsKey(taskId))
{
OpenTaskInfo info = openTasks[taskId];
info.Result.SetResult(completedEvent.Result);

openTasks.Remove(taskId);
}
```

// write event and in the else here. also do the same in other similar places in TaskOrchestrationContext
}