fsck: detect submodule urls starting with dash

Urls with leading dashes can cause mischief on older
versions of Git. We should detect them so that they can be
rejected by receive.fsckObjects, preventing modern versions
of git from being a vector by which attacks can spread.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
static char *get_object_name(struct fsck_options *options, struct object *obj)
{
	if (!options->object_names)
		return NULL;
	return lookup_decoration(options->object_names, obj);
}

static char *get_object_name(struct fsck_options *options, struct object *obj)
{
	if (!options->object_names)
		return NULL;
	return lookup_decoration(options->object_names, obj);
}
