Update appearance.js ImprovedTube.descriptionSidebar undefined

[raszpl]

ImprovedTube.descriptionSidebar was undefined without undoTheNewSidebar, this is why proper code indentation is so important, just clicking auto align in IDE would reveal this bug

[ImprovedTube]

indentation! yay! yay

[ImprovedTube]

about this code btw:
comparison: btw: #2251 and:

www.youtube.com##+js(set, yt.config_.EXPERIMENT_FLAGS.kevlar_watch_grid, false)
www.youtube.com##+js(set, yt.config_.EXPERIMENT_FLAGS.small_avatars_for_comments, false)
www.youtube.com##+js(set, yt.config_.EXPERIMENT_FLAGS.small_avatars_for_comments_ep, false)

thanks to @PoorChameleon #2038 (comment)

[raszpl]

the way uBO 'set' works is they put a Proxy over object prototypes
https://github.com/gorhill/uBlock/blob/c154aaa69c6a2a4009d43923f1097c6298062b82/assets/resources/scriptlets.js#L556-L586
they even hide proxy presence so YT cant detect it (afaik YT doesnt try, but plenty of shady websites try to detect adblock/overrides) https://github.com/gorhill/uBlock/blob/c154aaa69c6a2a4009d43923f1097c6298062b82/assets/resources/scriptlets.js#L578-L580

This way no matter what inside real yt.config_.EXPERIMENT_FLAGS.kevlar_watch_grid any reader will always receive overridden value. We can definitely implement this, much saner, safer and more reliable than blindly writing to yt.config_.EXPERIMENT_FLAGS.kevlar_watch_grid hoping
1 its there
2 it wasnt read by YT engine yet