Fix issue with ros2bag record python frontend (#100)

* Update record.py

Add _subparser member variable ( which is being called at line number 94). Otherwise it causes segmentation fault on calling ros2 bag record.

Signed-off-by: Sagnik <basusagnik1995@gmail.com>

* Update record.py

Add type info to parser

Signed-off-by: Sagnik <basusagnik1995@gmail.com>

ros2bag/ros2bag/verb/record.py

@@ -48,10 +48,12 @@ def add_arguments(self, parser, cli_name):  # noqa: D102
             help='disables topic auto discovery during recording: only topics present at '
              'startup will be recorded')
         parser.add_argument(
-            '-p', '--polling-interval', default=100,
+            '-p', '--polling-interval', type=int, default=100,
             help='time in ms to wait between querying available topics for recording. It has no '
              'effect if --no-discovery is enabled.'
         )
+        self._subparser = parser
+
 
     def create_bag_directory(self, uri):
         try: