IteratorStep result == done cannot be passed to IteratorValue

[woess]

In the following spec text, passing the result of IteratorStep to IteratorValue does not make sense, since if the iterator is done, the return value of IteratorStep is DONE, not the iterator result object expected by IteratorValue:

proposal-iterator-sequencing/spec.emu

Lines 28 to 30 in 5731124

	1. Let _iteratorResult_ be ? IteratorStep(_iteratorRecord_).
	1. If _iteratorResult_ is ~done~, then
	1. Perform ? IteratorValue(_iteratorResult_).

To fix this, IteratorStep probably has to be replaced with explicit IteratorNext and IteratorComplete calls.