Update MarkupSitemapXML.module

fixed issue with LanguageLocalizedURL module.

Sorry for the back and forth, but had to fix it or I couldn't sleep ;)

I tested again to make sure everything works. There's might be some constellation that it may could break it but I haven't found any major issues.

You can get language sitemaps with  /en/sitemap.xml, /de/sitemap.xml