C#: Fix processing exclusions during export

[shana]

When I added the filtering logic to allow excluding files or directories from the export logic, I made a mistake in the logic around deciding whether to recurse into a directory or not - it was only called if the directory itself was ignored. The intended logic should be:

• filterDir - Process this directory?
  • if false: stop processing this directory tree
  • if true:
    • call addEntry to allow doing something with the directory entry itself
    • recurseDir - Process the contents of this directory?
      • if false: stop processing this directory tree
      • if true: recursively process this directory

This PR fixes that.

/cc @raulsntos @RedworkDE

Contrbuted by W4Games ❤️

[raulsntos]

LGTM. Thanks!

[akien-mga]

Thanks!