Fix `XML::write()` for comments in root element
Fix `XML::write()` for comments in root element

See #2545

SoftCreatR/WCF,MenesesEvandro/WCF,Cyperghost/WCF,Cyperghost/WCF,Cyperghost/WCF,WoltLab/WCF,Cyperghost/WCF,WoltLab/WCF,WoltLab/WCF,SoftCreatR/WCF,MenesesEvandro/WCF,Cyperghost/WCF,SoftCreatR/WCF,SoftCreatR/WCF,WoltLab/WCF