The strbuf used in add_submodule_odb() was never released. So for every
submodule - populated or not - we leaked its object directory name when
using "git diff*" with the --submodule option.
Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>