Telepathy: ignore errors from ack_all_pending_messages()

Invalid ID errors from that function are normal, because the set
of IDs to acknowledge may not match the set in the connection manager
due to race conditions.
This is also what empathy does.

https://bugzilla.gnome.org/show_bug.cgi?id=683449

js/ui/components/telepathyClient.js

@@ -730,8 +730,7 @@ const ChatSource = new Lang.Class({
     _ackMessages: function() {
         // Don't clear our messages here, tp-glib will send a
         // 'pending-message-removed' for each one.
-        this._channel.ack_all_pending_messages_async(Lang.bind(this, function(src, result) {
-            this._channel.ack_all_pending_messages_finish(result);}));
+        this._channel.ack_all_pending_messages_async(null);
     }
 });