Skip locale update for system user

When the user profile document is created or modified, the listener UserLocaleSelectorListener is called to update the locale in the current user session. However such an update is useless for the system user which is not meant to log in to the platform.

Hence the locale update should be skipped when the current user is system.

Besides that, not updating the locale seems to prevent from side errors when trying the read the user workspace in custom unrestricted sessions.