fix corner case with nameCache (#3338)

fixes #3301

lib/scope.js

@@ -309,8 +309,12 @@ function names_in_use(scope, options) {
     if (!names) {
         scope.names_in_use = names = Object.create(scope.mangled_names || null);
         scope.cname_holes = [];
+        var cache = options.cache && options.cache.props;
         scope.enclosed.forEach(function(def) {
             if (def.unmangleable(options)) names[def.name] = true;
+            if (def.global && cache && cache.has(def.name)) {
+                names[cache.get(def.name)] = true;
+            }
         });
     }
     return names;