promisor-remote: reject empty name or URL in advertised remote

promisor-remote: reject empty name or URL in advertised remote

In parse_one_advertised_remote(), we check for a NULL remote name and
remote URL, but not for empty ones. An empty URL seems possible as
url_percent_decode("") doesn't return NULL.

In promisor_config_info_list(), we ignore remotes with empty URLs, so a
Git server should not advertise remotes with empty URLs. It's possible
that a buggy or malicious server would do it though.

So let's tighten the check in parse_one_advertised_remote() to also
reject empty strings at parse time.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>