git remote: allow adding remotes agreeing with url.<...>.insteadOf

When adding a remote, we make sure that the remote does not exist already. However, this test was not quite correct: when the url.<...>.insteadOf config variable was set to the remote name to be added, the code would assume that the remote exists already. Let's allow adding remotes when there is a url.<...>.insteadOf setting when both the name and the URL agree with the remote to be added. It might seem like a mistake to compare against remote->url[0] without verifying that remote->url_nr >=1, but at this point a missing URL has been filled by the name already, therefore url_nr cannot be zero. Noticed by Anastas Dancha. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>