builder: internals: fix incomplete chown walk when fixing permissions

This patch fixes the permission fixing code used by addContext, which
would not be responsible for Lchown-ing top-level directories added to a
destination that didn't exist prior to untar-ing the context.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> (github: cyphar)
Merge pull request #9616 from cyphar/9608-builder-fix-incomplete-chown-walk-addcontext

builder: internals: fix incomplete chown walk when fixing permissions