check if nginx site dir exist

debian/postinst

@@ -151,6 +151,8 @@ EOF
       ucf --debconf-ok --three-way ${gitlab_debian_conf_private} ${gitlab_debian_conf}
       ucfr gitlab ${gitlab_debian_conf}
 
+      # configure nginx site
+      if test -d /etc/nginx/sites-available/; then
         if test -f ${nginx_conf_example}; then
           nginx_site="/etc/nginx/sites-available/${GITLAB_HOST}"
           sed -e "s/YOUR_SERVER_FQDN/${GITLAB_HOST}/"\
@@ -163,6 +165,7 @@ EOF
           echo "nginx example configuration file not found"
           exit 1
         fi
+      fi
       # Reload nginx
       if command -v nginx > /dev/null; then
         echo "Reloading nginx configuration..."