fix for http://forum.yacy-websuche.de/viewtopic.php?p=21439#p21439

git-svn-id: https://svn.berlios.de/svnroot/repos/yacy/trunk@7390 6c8d7289-2bf4-0310-a012-ef5d649a1542

source/net/yacy/kelondro/rwi/IndexCell.java

@@ -303,12 +303,11 @@ public final class IndexCell<ReferenceType extends Reference> extends AbstractBu
             for (byte[] b: failedURLs.keySet()) try {words.put(b);} catch (RowSpaceExceededException e) {}
         }
 
-        for (byte[] b: words) {
-            HandleSet urls;
         synchronized (failedURLs) {
-                urls = failedURLs.remove(b);
+            for (byte[] b: words) {
+                HandleSet urls = failedURLs.remove(b);
+                if (urls != null) remove(b, urls);
             }
-            remove(b, urls);
         }
         this.countCache.clear();
     }