Fix for NullPointer where a run starts but there's nothing to do (no shards) and reduceInit() wasn't being called correctly

git-svn-id: file:///humgen/gsa-scr1/gsa-engineering/svn_contents/trunk@5096 348d0f76-0448-11de-a6fe-93d51630548a

java/src/org/broadinstitute/sting/gatk/executive/Accumulator.java

@@ -126,7 +126,7 @@ public abstract class Accumulator {
          * The result of the traversal is the list of accumulated intervals.
          */
         public Object finishTraversal() {
-            walker.onTraversalDone(accumulator);
+            walker.onTraversalDone(getReduceInit());  // must call getReduceInit to ensure that we get the accumulator value or the reduceInit value
             return this.accumulator;
         }
     }