Issue 6437 - Do not override scheduled full processing

lib/content/elemHideEmulation.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 705 matching lines @@
         this.queueFiltering(params.stylesheets, params.mutations);
       }
     };
 
     if (this._scheduledProcessing)
     {
       if (!stylesheets && !mutations)
       {
         this._scheduledProcessing = {};
       }
-      else
+      else if (this._scheduledProcessing.stylesheets ||
+               this._scheduledProcessing.mutations)
       {
         if (stylesheets)
         {
           if (!this._scheduledProcessing.stylesheets)
             this._scheduledProcessing.stylesheets = [];
           this._scheduledProcessing.stylesheets.push(...stylesheets);
         }
         if (mutations)
         {
           if (!this._scheduledProcessing.mutations)
@@ skipping 71 matching lines @@
           characterData: shouldObserveCharacterData(this.patterns),
           subtree: true
         }
       );
       this.document.addEventListener("load", this.onLoad.bind(this), true);
     }
   }
 };
 
 exports.ElemHideEmulation = ElemHideEmulation;