Issue 4802 - Add back compatibility for Microsoft Edge after #4722 removed it

options.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 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 38 matching lines @@
     if (arguments.length > 0)
     {
       var lastArg = arguments[arguments.length - 1];
       if (typeof lastArg == "function")
         callback = lastArg;
 
       for (var i = 0; i < arguments.length - (callback ? 1 : 0); i++)
         message[paramKeys[i]] = arguments[i];
     }
 
-    ext.backgroundPage.sendMessage(message, callback);
+    // Edge silently fails when sendMessage is called with a callback
+    // parameter of undefined, so we work around that here.
+    if (callback)
+      ext.backgroundPage.sendMessage(message, callback);
+    else
+      ext.backgroundPage.sendMessage(message);
   };
 }
 
 var getDocLink = wrapper({type: "app.get", what: "doclink"}, "link");
 var getInfo = wrapper({type: "app.get"}, "what");
 var getPref = wrapper({type: "prefs.get"}, "key");
 var togglePref = wrapper({type: "prefs.toggle"}, "key");
 var getSubscriptions = wrapper({type: "subscriptions.get"},
                                "downloadable", "special");
 var removeSubscription = wrapper({type: "subscriptions.remove"}, "url");
@@ skipping 657 matching lines @@
       onFilterMessage(message.action, message.args[0]);
       break;
     case "prefs.respond":
       onPrefMessage(message.action, message.args[0]);
       break;
     case "subscriptions.respond":
       onSubscriptionMessage(message.action, message.args[0]);
       break;
   }
 });