fix corner case in rename (#3481)

fixes #3480

lib/mozilla-ast.js

@@ -403,7 +403,7 @@
         var def = M.definition();
         return {
             type: "Identifier",
-            name: def ? def.mangled_name || def.name : M.name
+            name: def && def.mangled_name || M.name
         };
     });
 

lib/output.js

@@ -1355,7 +1355,7 @@ function OutputStream(options) {
     });
     DEFPRINT(AST_Symbol, function(self, output) {
         var def = self.definition();
-        output.print_name(def ? def.mangled_name || def.name : self.name);
+        output.print_name(def && def.mangled_name || self.name);
     });
     DEFPRINT(AST_Hole, noop);
     DEFPRINT(AST_This, function(self, output) {

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;
         });
     }
 });