fix corner case with arguments (#4697)

fixes #4696

lib/ast.js

@@ -428,7 +428,7 @@ var AST_For = DEFNODE("For", "init condition step", {
 }, AST_IterationStatement);
 
 var AST_ForEnumeration = DEFNODE("ForEnumeration", "init object", {
-    $documentation: "Base class for enumeration loops, i.e. `for ... in`, `for ... of` &  `for await ... of`",
+    $documentation: "Base class for enumeration loops, i.e. `for ... in`, `for ... of` & `for await ... of`",
     $propdoc: {
         init: "[AST_Node] the assignment target during iteration",
         object: "[AST_Node] the object to iterate over"

lib/scope.js

@@ -108,6 +108,7 @@ function is_lhs(node, parent) {
     if (parent instanceof AST_DefaultValue) return parent.name === node && node;
     if (parent instanceof AST_Destructured) return node;
     if (parent instanceof AST_DestructuredKeyVal) return node;
+    if (parent instanceof AST_ForEnumeration) return parent.init === node && node;
     if (parent instanceof AST_Unary) return unary_side_effects[parent.operator] && parent.expression;
 }