Throw error if config.json is not found

[SaiiDey]

In PsfRuntime/Config.cpp we have function load_json. We try multiple locations where we expect config.json. But if config.sjon is not found anywhere, we don't get proper error. It simply crashes. Check the for loop. We don't check if file is still null after exiting the for loop but that is a valid outcome from the code flow.