Upgrade from 4.6.3 to 4.6.4 not completed
You can see exactly what queries are being run by this incremental upgrade by opening up the CRM/Upgrade/Incremental/sql/4.6.4.mysql.tpl. In this case it's basically nothing. There is one query in there, which you could copy and paste into e.g. PHPMyAdmin and run it from there (although it honestly doesn't look very important).

Normally I would worry about a hung upgrade and recommend you restore from backups and try again. But in this case I think you lucked out.