Issue 4579 - Do not wrap non-existent APIs

polyfill.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 49 matching lines @@
 
     for (let node of path)
     {
       object = object[node];
 
       if (!object)
         return;
     }
 
     let func = object[name];
+    if (!func)
+      return;
+
     object[name] = function(...args)
     {
       let callStack = new Error().stack;
 
       if (typeof args[args.length - 1] == "function")
         return func.apply(object, args);
 
       // If the last argument is undefined, we drop it from the list assuming
       // it stands for the optional callback. We must do this, because we have
       // to replace it with our own callback. If we simply append our own
@@ skipping 57 matching lines @@
 
   // Workaround since HTMLCollection, NodeList, StyleSheetList, and CSSRuleList
   // didn't have iterator support before Chrome 51.
   // https://bugs.chromium.org/p/chromium/issues/detail?id=401699
   for (let object of [HTMLCollection, NodeList, StyleSheetList, CSSRuleList])
   {
     if (!(Symbol.iterator in object.prototype))
       object.prototype[Symbol.iterator] = Array.prototype[Symbol.iterator];
   }
 }