implement isPayloadAvailable (just return false, payloads unimplemented here), b/c it desn't compile without it.

git-svn-id: https://svn.apache.org/repos/asf/lucene/java/trunk@535361 13f79535-47bb-0310-9956-ffa450edef68

contrib/memory/src/java/org/apache/lucene/index/memory/MemoryIndex.java

@@ -911,6 +911,11 @@ public class MemoryIndex {
           throw new UnsupportedOperationException();
         }
 
+        public boolean isPayloadAvailable() {
+          // unsuported
+          return false;
+        }
+
       };
     }