xmlMode and tag literal in CSS comments

node v10.11.0
juice v5.0.0

Attempted to reproduce on tonic / RunKit:
https://runkit.com/embed/1miy61szoz0h

CSS comments containing HTML tag literals result in mangled markup (see the `` following the style declaration) and no inlining.

````js
const juice = require('juice');

const options = {
xmlMode: true
};

const html = `



/* <div> Tag literal in comment */
div {
color: red;
}

`;

console.log(juice(html, options));
````

returns

````html

/* <div> Tag literal in comment */
div {
color: red;
}
</div>

````

Start by running the provided juice(html, options) reproduction with xmlMode enabled and compare the malformed closing tag and missing inlining with the expected output. Trace the handling of CSS comments and style markup, then verify that tag literals in comments no longer alter the surrounding HTML and that the div rule is inlined.

Written by the indexing model from the issue text.