(fix) return default settings when no tsconfig found

[dummdidumm]

This prevents the code from being transpiled as es3 in this situation, which makes the const $$$$$ = .. separator get transformed into var $$$$$ = ... which then is no longer split out. This situation came up in the tests of svelte-jester.
No test added, because it's not really possible, because there's a tsconfig in this repo which would be found.

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Tests

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[kaisermann]

Thanks 🎉 Released in v4.9.5