FastMove does not mark the task as finished

When option to read task size before blocking is set to true, CH tries to scan the source to determine the size of task to process. But in case the operation is move (and not copy), there is an additional subtask just before the size scanning - it's fast move.
It might just happen that the fast move will finish all task has to do with this pre-scan.
We don't mark the task as complete, even if it was completed already.

To do: after performing pre-scan, check if all paths are marked as processed. In that case do not block processing.