Do not automatically skip directory entries

[bicobus]

Directories might be empty and required by whatever is contained in the archive, as such skipping them from being included in the list of files shouldn't be a default behavior.

More over, the __init__ of Archive7z is so large that extending the class to circumvent that behavior is practically not possible.

Relevant code: https://github.com/fancycode/pylzma/blob/ccb0e7cff3f6ecd5d38e73e9ca35502d7d670176/py7zlib.py#L983-L986