status/keyboard: Only change the current source setting if it changed

This avoids all the work that goes on in various processes when
switching input sources if the activated source is the currently
configured one.

https://bugzilla.gnome.org/show_bug.cgi?id=691414

js/ui/status/keyboard.js

@@ -470,6 +470,8 @@ const InputSourceIndicator = new Lang.Class({
             let is = new InputSource(type, id, displayName, shortName, i);
 
             is.connect('activate', Lang.bind(this, function() {
+                if (this._currentSource.index == is.index)
+                    return;
                 this._settings.set_value(KEY_CURRENT_INPUT_SOURCE,
                                          GLib.Variant.new_uint32(is.index));
             }));