wpmu_validate_blog_signup does not check the current site, but the one with id == 1

[larysa]

default WP blog validation procedure wpmu_validate_blog_signup () only checks the first site ( id == 1 and in the case of multisite install skips the check for the current main site)

file: wp-includes/ms-functions.php function: wpmu_validate_blog_signup

calls: domain_exists($mydomain, $path)

should check: domain_exists($mydomain, $path, $current_site->id)

[wonderboymusic]

Keywords has-sergey added.

[nacin]

Looks good.

[nacin]

In [21853]:

Pass current network ID to domain_exists() in wpmu_validate_blog_signup(). props larysa, fixes #17303.