check for at-end-of-data in iterator init. patch by jbellis; reviewed by Jun Rao for CASSANDRA-153

git-svn-id: https://svn.apache.org/repos/asf/incubator/cassandra/trunk@773727 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/cassandra/db/FileStruct.java

@@ -184,7 +184,14 @@ public class FileStruct implements Comparable<FileStruct>, Iterator<String>
                     forward();
                 }
             }
-            saved = key;
+            if (key.equals(SSTable.blockIndexKey_))
+            {
+                saved = null;
+            }
+            else
+            {
+                saved = key;
+            }
         }
 
         private void forward()