merge -r1287 from branch-1_6 to trunk

bug 349: Nicer display messages instead of "die" when urls cannot be 
solved (also set 404 status code for bots)

git-svn-id: http://piwigo.org/svn/trunk@1288 68402e56-0260-453c-a942-63ccdbb3a9ee

include/functions_category.inc.php

@@ -118,6 +118,8 @@ SELECT '.implode(',', $infos).'
   WHERE id = '.$id.'
 ;';
   $row = mysql_fetch_array(pwg_query($query));
+  if (empty($row))
+    return null;
 
   $cat = array();
   foreach ($infos as $info)