Use childNodes[2] for finding file resolution

ExLinks support vanilla 4chan and can add in its reverse image search link to the .fileText before 4chan X manages to parse it. As a result, 4chan X ends up looking at the reverse image search link for dimensions instead of the correct text element. Using childNodes[2] instead of lastChild fixes this.
Build pathnames taking into account the thread slug.
Merge pull request #1603 from Hupotronic/parsefile-fix

Use childNodes[2] for finding file resolution
Don't hide hr.desktop in threads.
Don't mess with the wrong <hr>.
Changelog.
Release 4chan X v3.20.11.