todo-app/final: utils.py needs check on table existence before accessing, or Exception handler

[mike-whittaker-work]

List of table entries
`python users.py -l

Traceback (most recent call last):
File "users.py", line 86, in
main()
File "users.py", line 80, in main
list_users(args.stage)
File "users.py", line 53, in list_users
for item in table.scan()['Items']:
File "xxx/venv/lib/python3.8/site-packages/boto3/resources/factory.py", line 520, in do_action
response = action(self, *args, **kwargs)
File "xxx/venv/lib/python3.8/site-packages/boto3/resources/action.py", line 83, in call
response = getattr(parent.meta.client, operation_name)(*args, **params)
File "xxx/venv/lib/python3.8/site-packages/botocore/client.py", line 316, in _api_call
return self._make_api_call(operation_name, kwargs)
File "xxx/venv/lib/python3.8/site-packages/botocore/client.py", line 635, in _make_api_call
raise error_class(parsed_response, operation_name)
botocore.errorfactory.ResourceNotFoundException: An error occurred (ResourceNotFoundException) when calling the Scan operation: Requested resource not found
`