HTML considered invalid wrongly.

When trying to parse hte html from [this page](https://pkg.go.dev/github.com/astaxie/beego#section-readme), calls to `valid` returns false and the HTML isn't parsed.

Further inspection shows that the call to `base_parse` returns a stack of length 21, let me thinking that the closing tags aren't appropriately detected.

I used version `6.1.13`.