[TIMOB-19062] Windows: CommandBar does not work with TabGroup

var tabGroup = Titanium.UI.createTabGroup();

var win1 = Titanium.UI.createWindow({
    title: 'Tab 1',
    backgroundColor: '#fff'
});
var tab1 = Titanium.UI.createTab({
    icon: 'KS_nav_views.png',
    title: 'Tab 1',
    window: win1
});

var label1 = Titanium.UI.createLabel({
    color: '#999',
    text: 'I am Window 1',
    font: { fontSize: 20, fontFamily: 'Helvetica Neue' },
    textAlign: 'center',
    width: 'auto'
});

win1.add(label1);

var platform = Ti.Platform.osname;
if (platform === 'windowsphone' || platform === 'windowsstore') {
    // Windows command bar
    var commandBar = Ti.UI.Windows.createCommandBar();
    var addButton = Ti.UI.Windows.createAppBarButton({ icon: Ti.UI.Windows.SystemIcon.ADD, touchEnabled: true });
    addButton.addEventListener('click', function () {
        alert('clicked');
    });
    commandBar.items = [addButton];
    win1.add(commandBar);
}

tabGroup.addTab(tab1);
tabGroup.open();