Use task_id in generating the queue file path

Use task_id in generating the queue file path

The task_id is created anyway as a UUID. So it is very
unique per definition. The only thing needed for the queue
file path is a unique part.

Before the objectid of the MediaEntry was used instead. But
in the sql world the objectid is only available after an
"insert" on the db. And creating the queue_file_path
afterwards would require an "update" on the db. We can save
that. ... for now.