Tuple union types incorrectly infer never type

separated from #22432

TypeScript Version: 2.7.0-dev.20180307

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Code

type C<R> = [R[]] | [R[], void];
declare function h<T>(f: C<T>): void;
h([[]] as [never[]]); // T: never[]
h([[]] as [void[]]); // T: void

Expected behavior:

h([[]] as [never[]]); // T: never
h([[]] as [void[]]); // T: void

Actual behavior:

h([[]] as [never[]]); // T: never[]
h([[]] as [void[]]); // T: void

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