path: Fix `git_path_walk_up` to work with non-rooted paths
attr: Add an extra test for files under a subfolder
attr: Do not walk path if we're at the root
Style
repository: Do not double-free config
Merge pull request #2571 from libgit2/vmg/walk-up-path

Fix `git_path_walk_up` to work with non-rooted paths