fix(admin_audit): Do not log errors for new files

[juliusknorr]

Avoid logging an error for cases when the audit log is triggered on a new file during the BeforeNodeReadEvent as in this case we get an NonExistingFile as the file has no file id yet

Sample error trace:

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)