Switching to Scratch causes challenge to hang

[navzam]

Repro steps:

1. Start a challenge
2. Switch programming language to Scratch
3. "Loading..." screen appears and never goes away. There doesn't seem to be any way to recover the challenge (refreshing challenge, switching to another scene and coming back to the challenge, etc.)

I think it has to do with currentLanguage being set to "scratch", but code doesn't have "scratch" as a key, so in this code:

Simulator/src/pages/ChallengeRoot.tsx

Lines 807 to 812 in 9976b18

	const language = this.currentLanguage;
	const code = language ? this.code[language] : undefined;
	if (!scene || scene.type === Async.Type.Unloaded || !language || !code) {
	return <Loading />;
	}

!code is always true