fixed null pointer exception

See http://www.yacy-forum.de/viewtopic.php?p=25598#25598

git-svn-id: https://svn.berlios.de/svnroot/repos/yacy/trunk@2588 6c8d7289-2bf4-0310-a012-ef5d649a1542

source/de/anomic/plasma/plasmaWordIndexAssortment.java

@@ -270,7 +270,7 @@ public final class plasmaWordIndexAssortment {
         private Iterator rowIterator;
         
         public containerIterator(String startWordHash, boolean up, boolean rot) throws IOException {
-            rowIterator = assortments.rows(up, rot, startWordHash.getBytes());
+            rowIterator = assortments.rows(up, rot, (startWordHash == null) ? null : startWordHash.getBytes());
         }
         
         public boolean hasNext() {