Merge pull request mikemccand#43 from atris/fix_execservicecleanup

Close Executorservice Only when Concurrent Search Was Used

Author: mikemccand

src/main/perf/SearchPerfTest.java

@@ -581,7 +581,10 @@ public void run() {
       allTasks.clear();
     }
 
-    executorService.shutdownNow();
+    if (executorService != null) {
+      executorService.shutdownNow();
+    }
+
     mgr.close();
 
     if (taxoReader != null) {