Fix bug: Prevent mis-application of Implicit Normal Completion

Currently, `_blockValue_` is subject to implicit NormalCompletion,
but this isn't valid when it's an abrupt completion.

Author: jmdyck

spec.html

@@ -21076,7 +21076,7 @@ <h1>Runtime Semantics: Evaluation</h1>
         1. Set the running execution context's LexicalEnvironment to _blockEnv_.
         1. Let _blockValue_ be Completion(Evaluation of |StatementList|).
         1. Set the running execution context's LexicalEnvironment to _oldEnv_.
-        1. Return _blockValue_.
+        1. Return ? _blockValue_.
       </emu-alg>
       <emu-note>
         <p>No matter how control leaves the |Block| the LexicalEnvironment is always restored to its former state.</p>