fix external gby to not open the writer twice

git-svn-id: https://hyracks.googlecode.com/svn/branches/fullstack_asterix_stabilization@3110 123451ca-8445-de46-9d55-352943316053
diff --git a/hyracks/hyracks-dataflow-std/src/main/java/edu/uci/ics/hyracks/dataflow/std/group/HashSpillableTableFactory.java b/hyracks/hyracks-dataflow-std/src/main/java/edu/uci/ics/hyracks/dataflow/std/group/HashSpillableTableFactory.java
index f2b56fa..f86d9fb 100644
--- a/hyracks/hyracks-dataflow-std/src/main/java/edu/uci/ics/hyracks/dataflow/std/group/HashSpillableTableFactory.java
+++ b/hyracks/hyracks-dataflow-std/src/main/java/edu/uci/ics/hyracks/dataflow/std/group/HashSpillableTableFactory.java
@@ -256,8 +256,6 @@
 
                 outputAppender.reset(outputFrame, true);
 
-                writer.open();
-
                 if (tPointers == null) {
                     // Not sorted
                     for (int i = 0; i < tableSize; ++i) {