Fix #516 - Chown not suported on Windows (#518)
Fix #516 - Chown not suported on Windows (#518)

Proposed fix for #516: Do not attempt to call `os.Chown` on Windows. The
command is unsupported on windows and will always return
`syscall.EWINDOWS`.

Handling for user ID and group ID on Windows already hardcodes
both values to zero. If a snapshot is restored with non-zero UID/GID
values (for instance if the snapshot was created on a different OS),
filesystem entries will be restored without changing UID/GID, resulting
in a state similar to how they would look if the snapshot was
taken on Windows in the first place.
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