Editorial: Add a Return step to ModuleDeclarationEnvironmentSetup (#1266

)

When control exits the bottom of the algorithm,
the return value isn't defined.
This wouldn't matter if the operation were invoked
with a simple "Perform", but it's invoked as:
    Perform ? ModuleDeclarationEnvironmentSetup(_module_)
and the '?' (i.e., ReturnIfAbrupt) will examine the return value,
so it should be well-defined.

Any non-abrupt return will do.

spec.html

@@ -22198,6 +22198,7 @@ <h1>ModuleDeclarationEnvironmentSetup ( _module_ )</h1>
                   1. If _d_ is a |FunctionDeclaration|, a |GeneratorDeclaration|, an |AsyncFunctionDeclaration|, or an |AsyncGeneratorDeclaration|, then
                     1. Let _fo_ be the result of performing InstantiateFunctionObject for _d_ with argument _env_.
                     1. Call _envRec_.InitializeBinding(_dn_, _fo_).
+              1. Return NormalCompletion(~empty~).
             </emu-alg>
           </emu-clause>
         </emu-clause>