Fix unique atom id and empty title

app/controllers/feed.scm

@@ -34,8 +34,8 @@
          (author (colt-conf-get 'blog-author)))
     `(entry
       (author (name ,author) (uri ,blog-url))
-      (title (@ (type "text")) ,title)
-      (id ,(string-append blog-url "/")) ; according to W3C validation to end with '/'
+      (title (@ (type "text")) ,(if (string-null? title) "No title" title))
+      (id ,(post-oid post))
       (link (@ (rel "alternate") (type "text/html")
                (href ,(->url blog-url url-name))))
       (published ,updated-time)