Raise an exception when handling unsafe content

We were confused about what `.html_safe` did, and were automatically
marking as safe content which was not.

app/helpers/text_with_links_helper.rb

@@ -8,8 +8,8 @@ module TextWithLinksHelper
 
   def auto_link_already_sanitized_html(html)
     return if html.nil?
-    html = ActiveSupport::SafeBuffer.new(html) if html.is_a?(String)
-    return html.html_safe unless html.html_safe?
+    raise "Could not add links because the content is not safe" unless html.html_safe?
+
     Rinku.auto_link(html, :all, 'target="_blank" rel="nofollow"').html_safe
   end