[gnome-shell/cherry-pick-74bb9e62] ibusManager: Don't pass undefined callback to ibus

[Marco Trevisan <marcotrevi src gnome org>]

commit 1045b35c8bec874f6db974ab6c4d1a9f37f24bf2
Author: Florian Müllner <fmuellner gnome org>
Date:   Thu Nov 15 17:47:55 2018 +0000

    ibusManager: Don't pass undefined callback to ibus
    
    Since commit 551e8278416, we don't always pass a callback parameter.
    However passing it on as undefined to ibus doesn't work, as gjs doesn't
    accept that as a valid callback value and throw an error. As a result,
    we can end up with no layout selected in the keyboard menu and an "empty"
    indicator. Fix this by explicitly passing null if no callback has been
    provided.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/293
    
    
    (cherry picked from commit 74bb9e62492bacda372904d30891eb97685e9b0c)

 js/misc/ibusManager.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/js/misc/ibusManager.js b/js/misc/ibusManager.js
index 6452e492f..ad2e0fc5a 100644
--- a/js/misc/ibusManager.js
+++ b/js/misc/ibusManager.js
@@ -205,7 +205,7 @@ var IBusManager = new Lang.Class({
         }
 
         this._ibus.set_global_engine_async(id, this._MAX_INPUT_SOURCE_ACTIVATION_TIME,
-                                           null, callback);
+                                           null, callback || null);
     },
 
     preloadEngines(ids) {