Fixed extraction loop to enable the extraction of "directory only" zip f...

...iles that are used to replicate empty (template) folder structures.

I know this "fix" has a small performance cost but it solves my problems and - in fact - makes Unzip act in a more concise way as it does not just "forget" about empty folders!

I did some benchmarking and calling CreateDirectory() a few times too often costs less than checking if we've got to create a folder first.

Hope this helps ;)