[LyX/master] DocBook: add assertion to help debugging.

[Thibaut Cuvelier]

commit 48a507694ea44d511da55917af64fa5dedabff37
Author: Thibaut Cuvelier <tcuvelier at lyx.org>
Date:   Thu Oct 7 02:34:07 2021 +0200

    DocBook: add assertion to help debugging.
---
 src/output_docbook.cpp |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/src/output_docbook.cpp b/src/output_docbook.cpp
index 50b66fb..e234d9d 100644
--- a/src/output_docbook.cpp
+++ b/src/output_docbook.cpp
@@ -754,6 +754,8 @@ DocBookDocumentSectioning hasDocumentSectioning(ParagraphList const &paragraphs,
 	bool documentHasSections = false;
 
 	while (bpit < epit) {
+		LASSERT(bpit < paragraphs.size(), return make_tuple(documentHasSections, bpit));
+
 		Layout const &style = paragraphs[bpit].layout();
 		documentHasSections |= isLayoutSectioningOrSimilar(style);