[Acrobat Reader]: checked attribute not working for <input type="radio"> unless its values are integers starting from 0

Checkboxes are generated but not checked. Nothing of `checked=""` or `checked="checked"` works. Just `checked` without value fails on parsing.

I tried my own file and an example from https://github.com/danfickle/openhtmltopdf/wiki/Form-Controls.

The trivial example of HTML file can look like this:
```

Radios checked test for PDF conversion

Radio 1
Radio 2

```

And the generated PDF will look like this:

Notably, the `checked` attribute works for the checkbox: