**Apache Airflow version**: 2.0.1

**Environment**:

- **Cloud provider or hardware configuration**: AWS

**What happened**:
I have Airflow with Cloudwatch-based remote logging running. I also have `BashOperator` that does, for example, `rsync` with invalid parameters, for example `rsync -av test test`. The output of the `rsync` error is formatted and contains empty line. Once that empty line is logged to the Cloudwatch, i receive an error:
```
2021-04-06 19:29:22,318] /home/airflow/.local/lib/python3.6/site-packages/watchtower/__init__.py:154 WatchtowerWarning: Failed to deliver logs: Parameter validation failed:
Invalid length for parameter logEvents[5].message, value: 0, valid range: 1-inf
[2021-04-06 19:29:22,320] /home/airflow/.local/lib/python3.6/site-packages/watchtower/__init__.py:158 WatchtowerWarning: Failed to deliver logs: None
```

So basically empty lines can't be submitted to the Cloudwatch and as result the whole output of the process doesn't appear in logs.

**What you expected to happen**:

I expect to have an output of the bash command in logs. Empty lines can be skipped or replaced with something.

**How to reproduce it**:

For example: run `BashOperator` with `rsync` command that fails on Airflow with Cloudwatch-based remote logging. It could be any other command that produces empty line in the output.
airflow/providers/amazon/aws/log/cloudwatch_task_handler.py
super().__init__(base_log_folder, filename_template)
        split_arn = log_group_arn.split(':')
        self.handler = None
        self.log_group = split_arn[6]
        self.region_name = split_arn[3]
        self.closed = False
    @cached_property
    def hook(self):
        """Returns AwsLogsHook."""
        remote_conn_id = conf.get('logging', 'REMOTE_LOG_CONN_ID')
        try:
            from airflow.providers.amazon.aws.hooks.logs import AwsLogsHook
            return AwsLogsHook(aws_conn_id=remote_conn_id, region_name=self.region_name)
        except Exception as e:
            self.log.error(
                'Could not create an AwsLogsHook with connection id "%s". '
                'Please make sure that apache-airflow[aws] is installed and '
                'the Cloudwatch logs connection exists. Exception: "%s"',
                remote_conn_id,
                e,
            )
            return None
    def _render_filename(self, ti, try_number):