align sliding algo with chunks/windows algos more and fix bug

Author: michaelficarra

spec.emu

@@ -55,13 +55,15 @@ copyright: false
       1. Repeat,
         1. Let _value_ be ? IteratorStepValue(_iterated_).
         1. If _value_ is ~done~, then
-          1. If _buffer_ is not empty and the number of elements in _buffer_ < ℝ(_windowSize_), perform ? Yield(CreateArrayFromList(_buffer_)).
+          1. If _buffer_ is not empty and the number of elements in _buffer_ < ℝ(_windowSize_), then
+            1. Perform Completion(Yield(CreateArrayFromList(_buffer_))).
           1. Return ReturnCompletion(*undefined*).
+        1. If the number of elements in _buffer_ is ℝ(_windowSize_), then
+          1. Remove the first element from _buffer_.
         1. Append _value_ to _buffer_.
         1. If the number of elements in _buffer_ is ℝ(_windowSize_), then
           1. Let _completion_ be Completion(Yield(CreateArrayFromList(_buffer_))).
           1. IfAbruptCloseIterator(_completion_, _iterated_).
-          1. Remove the first element from _buffer_.
     1. Let _result_ be CreateIteratorFromClosure(_closure_, *"Iterator Helper"*, %IteratorHelperPrototype%, « [[UnderlyingIterators]] »).
     1. Set _result_.[[UnderlyingIterators]] to « _iterated_ ».
     1. Return _result_.
@@ -84,11 +86,12 @@ copyright: false
       1. Repeat,
         1. Let _value_ be ? IteratorStepValue(_iterated_).
         1. If _value_ is ~done~, return ReturnCompletion(*undefined*).
+        1. If the number of elements in _buffer_ is ℝ(_windowSize_), then
+          1. Remove the first element from _buffer_.
         1. Append _value_ to _buffer_.
         1. If the number of elements in _buffer_ is ℝ(_windowSize_), then
           1. Let _completion_ be Completion(Yield(CreateArrayFromList(_buffer_))).
           1. IfAbruptCloseIterator(_completion_, _iterated_).
-          1. Remove the first element from _buffer_.
     1. Let _result_ be CreateIteratorFromClosure(_closure_, *"Iterator Helper"*, %IteratorHelperPrototype%, « [[UnderlyingIterators]] »).
     1. Set _result_.[[UnderlyingIterators]] to « _iterated_ ».
     1. Return _result_.