Issue 6183 - Avoid attempting to close the composer popup twice

composer.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 51 matching lines @@
 }
 
 function closeDialog(success)
 {
   browser.runtime.sendMessage({
     type: "forward",
     targetPageId,
     payload:
     {
       type: "composer.content.finished",
+      popupAlreadyClosed: true,
       remove: (typeof success == "boolean" ? success : false)
     }
   });
   closeMe();
 }
 
 function init()
 {
   // Attach event listeners
   window.addEventListener("keydown", onKeyDown, false);
@@ skipping 30 matching lines @@
         break;
       case "composer.dialog.close":
         closeMe();
         break;
     }
   });
 
   window.removeEventListener("load", init);
 }
 window.addEventListener("load", init, false);