Fix behavior of return on yield*.

test/mjsunit/harmony/generators-turbo.js

 // Copyright 2016 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.
 
 // Flags: --ignition --ignition-generators --harmony-do-expressions
 // Flags: --allow-natives-syntax --turbo --turbo-from-bytecode
 
 
 // This file is identical to mjsunit/harmony/generators.js, except for its Flags
 // lines. The purpose is to explicitly mention --turbo-from-bytecode such that
@@ skipping 625 matching lines @@
     while (true) {
       if (true || false) yield 42;
       continue;
     }
   }
   g = foo();
   assertEquals({value: 42, done: false}, Next(g));
   assertEquals({value: 42, done: false}, Next(g));
   assertEquals({value: 42, done: false}, Next(g));
 }
+
+{
+  let foo = function*() {
+    yield* (function*() { yield 42; }());
+    assertUnreachable();
+  }
+  g = foo();
+  assertEquals({value: 42, done: false}, Next(g));
+  assertEquals({value: 23, done: true}, Return(g, 23));
+}