merge r2921 from branch 2.0 to trunk

bug 907 fixed: avoid PHP warning when pwg.images.add adds a photo in a
category that either contains no "ranked" image or when category is empty.


git-svn-id: http://piwigo.org/svn/trunk@2922 68402e56-0260-453c-a942-63ccdbb3a9ee

include/ws_functions.inc.php

@@ -1613,6 +1613,11 @@ SELECT
 
       foreach ($cat_ids as $cat_id)
       {
+        if (!isset($current_rank_of[$cat_id]))
+        {
+          $current_rank_of[$cat_id] = 0;
+        }
+        
         if ('auto' == $rank_on_category[$cat_id])
         {
           $rank_on_category[$cat_id] = $current_rank_of[$cat_id] + 1;