Fix 500 when saving /site/edit without email
When saving /site/edit with no no_reply_email set, a 500 error page
would be returned due to an empty value being passed as value to
the datastore (which is not allowed for email fields).
<?xml version="1.0" encoding="UTF-8"?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
{% for location in sitemaps %}<sitemap><loc>{{ location }}</loc></sitemap>{% endfor %}
</sitemapindex>