removed duplicate fix for #4170 (from dd branch)

svn changeset:11717/svn branch:6.3

src/com/vaadin/data/util/IndexedContainer.java

@@ -568,10 +568,6 @@ public class IndexedContainer implements Container.Indexed,
                 return null;
             }
         }
-        if (index < 0) {
-            index = 0;
-        }
-
         return addItemAt(index, newItemId);
     }