Guard again potential nulls in `RealmNamedFileUsage`
Guard again potential nulls in `RealmNamedFileUsage`

Hopefully help in figuring out https://sentry.ppy.sh/organizations/ppy/issues/3679/?project=2&query=user%3A%22id%3A10078484%22

ppy/osu,ppy/osu,peppy/osu,peppy/osu,peppy/osu,ppy/osu