iso9660/finalize: parse empty path correctly
iso9660/finalize: parse empty path correctly

findEntry does not understand what to do when path.Dir returns "." on a
file with no directory. This happens when we don't pass a BootCatalog,
the default ones do not contain a path, or when we include a BootFile
without any path.

Signed-off-by: Morten Linderud <c55682c9a35d221382fd659854e9db84995087f2@mullvad.net>

diskfs/go-diskfs