Report unexpected lexical decl also without destructuring

test/message/let-lexical-declaration-destructuring-in-single-statement.js

 // Copyright 2017 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-with ({}) let [a] = [];
+with ({}) let [a] = [42];

[vabr (Chromium), 2017/02/17 09:52:07]

Note: I added an element in the list on the right-hand side, to highlight that
the important error here is the lexical decl replacing a single statement, not
the failure to destructure an empty list.

[Dan Ehrenberg, 2017/02/17 09:54:35]

Note that that wouldn't fail anyway.

[vabr (Chromium), 2017/02/17 10:55:46]

Ah, interesting. I see now that 'a' will become undefined.
This is due to
"3. If iteratorRecord.[[Done]] is true, let value be undefined."
in [1]'s AssignmentElement block, right?

[1]
https://tc39.github.io/ecma262/#sec-runtime-semantics-iteratordestructuringas...