only CreateAsyncFromSyncIterator when necessary

spec.html

@@ -162,20 +162,24 @@ <h1>
       <emu-alg>
         1. If _hint_ is not present, set _hint_ to ~sync~.
         1. If _iterator_ is either *undefined* or *null*, throw a *TypeError* exception.
+        1. Let _alreadyAsync_ be *false*.
         1. Let _method_ be *undefined*.
         1. If _hint_ is ~async~, then
           1. Set _method_ to ? GetV(_obj_, @@asyncIterator).
+          1. Set _alreadyAsync_ to *true*.
         1. If IsCallable(_method_) is *false*, then
           1. Set _method_ to ? GetV(_obj_, @@iterator).
+          1. Set _alreadyAsync_ to *false*.
         1. If IsCallable(_method_) is *false*, then
           1. Let _iterator_ be _obj_.
+          1. Set _alreadyAsync_ to *true*.
         1. Else,
           1. Let _iterator_ be ? Call(_method_, _obj_).
         1. If _iterator_ is not an Object, throw a *TypeError* exception.
         1. Let _nextMethod_ be ? Get(_iterator_, *"next"*).
         1. If IsCallable(_nextMethod_) is *false*, throw a *TypeError* exception.
         1. Let _iteratorRecord_ be the Iterator Record { [[Iterator]]: _iterator_, [[NextMethod]]: _nextMethod_, [[Done]]: *false* }.
-        1. If _hint_ is ~async~, then
+        1. If _hint_ is ~async~ and _alreadyAsync_ is *false*, then
           1. Return CreateAsyncFromSyncIterator(_iteratorRecord_).
         1. Return _iteratorRecord_.
       </emu-alg>