Fix listener unregister issue

It's a regression issue. The Python listener should be set to None when it fails to register.

Signed-off-by: Bobby Wang <[email protected]>

Author: wbo4958

nds/PysparkBenchReport.py

@@ -76,6 +76,7 @@ def _register_python_listener(self):
             listener.register()
         except TypeError as e:
             print("Not found com.nvidia.spark.rapids.listener.Manager", str(e))
+            listener = None
         return listener
 
     def _get_spark_conf(self):