* Handle pull events with complete progress details only
Under certain circumstances, Docker seems to send pull events with
incomplete progress details (i.e., missing 'current' or 'total' fields).
In practise, we've observed an empty dictionary for progress details
as well as missing 'total' field (while 'current' was present).
All events were using Docker 28.3.3 using the old, default Docker graph
backend.
* Fix docstring/comment