Make reserved names take priority over the name cache

lib/propmangle.js

@@ -140,10 +140,10 @@ function mangle_properties(ast, options) {
     // only function declarations after this line
 
     function can_mangle(name) {
+        if (reserved.indexOf(name) >= 0) return false;
         if (options.only_cache) {
             return cache.props.has(name);
         }
-        if (reserved.indexOf(name) >= 0) return false;
         if (/^[0-9.]+$/.test(name)) return false;
         return true;
     }