tree-diff: no need to call "full" diff_tree_sha1 from show_path()
As described in previous commit, when recursing into sub-trees, we can
use lower-level tree walker, since its interface is now sha1 based.
The change is ok, because diff_tree_sha1() only invokes
ll_diff_tree_sha1(), and also, if base is empty, try_to_follow_renames().
But base is not empty here, as we have added a path and '/' before
recursing.
Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru> Signed-off-by: Junio C Hamano <gitster@pobox.com>