I just noticed there is !672, which does the same thing (among other things). It seems inactive though and apparently has some issues.
My patch loads/uses the "parent folder" icon a bit differently, I'm not really sure how/why it works in the other patch. Otherwise, that portion of !672 seems to be very similar to my patch, with slightly different naming.
Since the "parent dir" button is probably the most pressing usability issue with that dialog and the other commit might be a bit too large, I'm keeping this merge request open.