Editorial: Add assertion that generatorKind is not non-generator (#3379)

Author: d01c2

spec.html

@@ -24254,6 +24254,7 @@ <h1>Runtime Semantics: Evaluation</h1>
       <emu-grammar>YieldExpression : `yield` `*` AssignmentExpression</emu-grammar>
       <emu-alg>
         1. Let _generatorKind_ be GetGeneratorKind().
+        1. Assert: _generatorKind_ is not ~non-generator~.
         1. Let _exprRef_ be ? Evaluation of |AssignmentExpression|.
         1. Let _value_ be ? GetValue(_exprRef_).
         1. Let _iteratorRecord_ be ? GetIterator(_value_, _generatorKind_).