[spec] fromHexInto/fromBase64Into: fix infinite loop

[ljharb]

Fixes #47

I'm not 100% sure this is the right fix, but it seems to be what your polyfill is doing, and the intention.

[bakkot]

Thanks! But it's +1, not +2

[ljharb]

ah, i assumed it's +2 because of

proposal-arraybuffer-base64/playground/polyfill-core.mjs

Line 280 in 2222881

index += 2;

[bakkot]

That line corresponds to the one in FromHex. The behavior in the loop in this PR is handled in the polyfill by using TA.prototype.set instead of copying one byte at a time.

[ljharb]

aha, thanks, makes sense.