AsyncResult.display_outputs should only print stdout/err if non-empty (single engine)

IPython/parallel/client/asyncresult.py

@@ -391,8 +391,9 b' class AsyncResult(object):'
         
         
     def _display_single_result(self):
-        
+        if self.stdout:
         print self.stdout
+        if self.stderr:
         print >> sys.stderr, self.stderr
         
         try: