XMLDocument can be a valid HTML document

[ameshkov]

Ads are not blocked on seclub.org
https://seclub.org/dn.php?d=4&r=6

For some reason this check does not work on this website:

        if (!(document instanceof HTMLDocument)) {
            return;
        }

document is XMLDocument there.

Use this instead:

var isHtml = function() { 
    return (document instanceof HTMLDocument) ||
        // https://github.com/AdguardTeam/AdguardBrowserExtension/issues/233
        ((document instanceof XMLDocument) && (document.createElement('div') instanceof HTMLDivElement)); 
};

[Mizzick]

Fixed