honour the Ad flag in newsfeeds

http://inn.eyrie.org/viewcvs/branches/2.4/innd/art.c?r1=7748&r2=7936&pathrev=7936&view=patch

--- 2.4/innd/art.c	2008/04/06 13:49:56	7748
+++ 2.4/innd/art.c	2008/07/20 10:20:41	7936
@@ -1725,7 +1725,7 @@
       !DISTwantany(sp->Distributions, list))
       /* Not in the site's desired list of distributions. */
       continue;
-    if (sp->DistRequired && list == NULL)
+    if (sp->DistRequired && (list == NULL || *list == NULL))
       /* Site requires Distribution header and there isn't one. */
       continue;