don't allow empty web_folder

interface/web/sites/form/web_vhost_domain.tform.php

interface/web/sites/lib/lang/ar_web_vhost_domain.lng

interface/web/sites/lib/lang/ar_web_vhost_subdomain.lng

interface/web/sites/lib/lang/bg_web_vhost_domain.lng

interface/web/sites/lib/lang/bg_web_vhost_subdomain.lng

interface/web/sites/lib/lang/br_web_vhost_domain.lng

interface/web/sites/lib/lang/br_web_vhost_subdomain.lng

interface/web/sites/lib/lang/ca_web_vhost_domain.lng

interface/web/sites/lib/lang/ca_web_vhost_subdomain.lng

interface/web/sites/lib/lang/cz_web_vhost_domain.lng

interface/web/sites/lib/lang/cz_web_vhost_subdomain.lng

interface/web/sites/lib/lang/de_web_vhost_domain.lng

interface/web/sites/lib/lang/de_web_vhost_subdomain.lng

interface/web/sites/lib/lang/dk_web_vhost_domain.lng

interface/web/sites/lib/lang/dk_web_vhost_subdomain.lng

interface/web/sites/lib/lang/el_web_vhost_domain.lng

interface/web/sites/lib/lang/el_web_vhost_subdomain.lng

interface/web/sites/lib/lang/en_web_vhost_domain.lng

interface/web/sites/lib/lang/en_web_vhost_subdomain.lng

interface/web/sites/lib/lang/es_web_vhost_domain.lng