fix & improve test/ufuzz.js (#2815)

- use correct `options` when testing `rename`
- mask arbitrarily assigned function IDs to reduce rate of false positives

test/ufuzz.js

@@ -1025,7 +1025,7 @@ function log_suspects(minify_options, component) {
 
 function log_rename(options) {
     if (!options.rename) return;
-    var m = JSON.parse(JSON.stringify(minify_options));
+    var m = JSON.parse(JSON.stringify(options));
     m.rename = false;
     var result = UglifyJS.minify(original_code, m);
     if (result.error) {