I recently added code for the zip packer to report progress, but there were some accidental omissions: three recursive calls missed out the $progress variable.

As a result it was possible that the progress callback did not get called between files when processing sub-folders.

As well as the fixes, I'm also adding a new unit test that covers this case that didn't work correctly before.

NOTE: There is still a long pause without progress calls in the zip archive 'close' method which is where it actually does most of the work, and because this ends up being a PHP built-in function we cannot do anything about it on a trivial level. I had some experimental work to improve this by closing it periodically but this is a bit inefficient; I think it's probably better to work on this issue with a new format as part of MDL-41838.