Avoid console error in html-preview-link

[fregante]

• Due to Run 50 more features before the whole page has loaded #6357 (comment)

refined-github.js:24847 Uncaught (in promise) TypeError: Cannot read properties of null (reading 'textContent')
    at isPublicRepo (refined-github.js:24847:88)
    at refined-github.js:17997:32
    at Array.every (<anonymous>)
    at shouldFeatureRun (refined-github.js:17997:19)
    at setupPageLoad (refined-github.js:3790:73)
    at Object.add (refined-github.js:3865:12)

Test URLs

https://github.com/OctoLinker/OctoLinker/commits/master