Fix desktop notification click handler for existing/new GMs (#5633)

webapp/stores/notification_store.jsx

@@ -71,7 +71,8 @@ class NotificationStoreClass extends EventEmitter {
             if (!channel) {
                 title = msgProps.channel_display_name;
                 channel = {
-                    name: msgProps.channel_name
+                    name: msgProps.channel_name,
+                    type: msgProps.channel_type
                 };
             } else if (channel.type === Constants.DM_CHANNEL) {
                 title = Utils.localizeMessage('notification.dm', 'Direct Message');