docbook reader: fix nesting of chapters and sections (#5864)

* Set dbBook to true when traversing a chapter too.
  Currently, a `<title/>` in a chapter and in a `<section/>` below that
  chapter have the same level if they're not inside a `<book/>`.

  This can happen in a multi-file book project. Also see the example at
  https://tdg.docbook.org/tdg/4.5/chapter.html

  Co-authored-by: Félix Baylac-Jacqué <felix@alternativebit.fr>

* Add docbook-chapter test

  This tests nested `<section/>` and makes sure `<title/>` in the first
  `<section/>` below `<chapter/>` is one level deeper than the `<chapter/>`'s
  `<title/>`, also when not inside a `<book/>`.

  Co-authored-by: Félix Baylac-Jacqué <felix@alternativebit.fr>

0 files changed, 0 insertions, 0 deletions