fix corner case in rename (#3481)

fixes #3480

lib/scope.js

@@ -511,13 +511,14 @@ AST_Toplevel.DEFMETHOD("expand_names", function(options) {
         if (def.global && options.cache) return;
         if (def.unmangleable(options)) return;
         if (options.reserved.has[def.name]) return;
-        var d = def.redefined();
-        def.name = d ? d.name : next_name();
+        var redef = def.redefined();
+        var name = redef ? redef.rename || redef.name : next_name();
+        def.rename = name;
         def.orig.forEach(function(sym) {
-            sym.name = def.name;
+            sym.name = name;
         });
         def.references.forEach(function(sym) {
-            sym.name = def.name;
+            sym.name = name;
         });
     }
 });