folded chapters don't expand with `highlight` in URL

[ehuss]

Problem

When opening a page in a book with folded chapters, and the highlight value in the URL, the chapter sidebar does not expand to unfold to that chapter.

Steps

Go directly to https://doc.rust-lang.org/nightly/rust-by-example/custom_types/enum.html?highlight=enums#enums

or

1. Go to https://doc.rust-lang.org/nightly/rust-by-example/
2. Type s to start a search, and enter "Enum"
3. Click on the first element

Notice that the sidebar does not expand:

It should expand (like it does if ?highlight=enums is not in the URL):

Possible Solution(s)

No response

Notes

cc @notriddle This seems to have regressed via #2414

Version

mdbook v0.4.48