Backport(v1.16) command: fix NoMethodError of --daemon under Windows (#…

…4796)

**Which issue(s) this PR fixes**: 

Backport #4716 

**What this PR does / why we need it**: 
To daemonize the process, the following code will be invoked on Windows:

https://github.com/fluent/fluentd/blob/89f0a76fb2e050659f0a503823beb2ad8cf899eb/lib/fluent/daemon.rb#L13

$log variable does not exist because it has not executed
`Superviser#setup_global_logger` method until here.
It will perform a new startup process and prepare a logger in

https://github.com/fluent/fluentd/blob/89f0a76fb2e050659f0a503823beb2ad8cf899eb/lib/fluent/daemon.rb#L13

This patch will only avoid the error since a logger is not required this
process.

**Docs Changes**:
Not needed.

**Release Note**: 
The same as the title.

Signed-off-by: Shizuo Fujita <[email protected]>
Signed-off-by: Kentaro Hayashi <[email protected]>
Co-authored-by: Watson <[email protected]>

lib/fluent/supervisor.rb

@@ -440,7 +440,7 @@ def self.serverengine_config(params = {})
         stop_immediately_at_unrecoverable_exit: true,
         root_dir: params['root_dir'],
         logger: $log,
-        log: $log.out,
+        log: $log&.out,
         log_level: params['log_level'],
         chuser: params['chuser'],
         chgroup: params['chgroup'],