sha1_file.c: move delayed getenv(altdb) back to setup_git_env()
getenv() is supposed to work on the main repository only. This delayed
getenv() code in sha1_file.c makes it more difficult to convert
sha1_file.c to a generic object store that could be used by both
submodule and main repositories.
Move the getenv() back in setup_git_env() where other env vars are
also fetched.
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>