fix corner case in ie8 (#4016)

fixes #4015

lib/scope.js

@@ -230,6 +230,7 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options) {
         } else {
             new_def = scope.def_variable(node);
         }
+        old_def.defun = new_def.scope;
         old_def.orig.concat(old_def.references).forEach(function(node) {
             node.thedef = new_def;
             node.reference(options);