Bug: taggedUnion doesn't handle sub unions / tagged unions correctly

[gcanti]

Repro

const A = t.type({ type: t.literal('A') })
const B = t.type({ type: t.literal('B') })
const C = t.type({ type: t.literal('C') })
const SubUnion = t.union([A, B])
const T = t.taggedUnion('type', [SubUnion, C])
console.log(T.decode({ type: 'B' }).isRight()) // false, should be true

const A = t.type({ type: t.literal('A') })
const B = t.type({ type: t.literal('B') })
const C = t.type({ type: t.literal('C') })
const SubTaggedUnion = t.taggedUnion('type', [A, B])
const T = t.taggedUnion('type', [SubTaggedUnion, C])
console.log(T.decode({ type: 'B' }).isRight()) // false, should be true