bundle: don't leak an fd in case of early return

bundle: don't leak an fd in case of early return

In successful operation `write_pack_data` will close the `bundle_fd`,
but when we exit early, we need to take care of the file descriptor
as well as the lock file ourselves. The lock file may be deleted at the
end of running the program, but we are in library code, so we should
not rely on that.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>