[LyX/master] Fix sign-compare warning

[Scott Kostyshak]

commit 1c70d98fc1b8cb8b89dba7089f2373a181b41e08
Author: Scott Kostyshak <skostysh at lyx.org>
Date:   Thu Oct 14 23:31:14 2021 -0400

    Fix sign-compare warning
    
    Fix warning comparing long int to long unsigned int.
---
 src/output_docbook.cpp |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/src/output_docbook.cpp b/src/output_docbook.cpp
index f35b82e..71d3b83 100644
--- a/src/output_docbook.cpp
+++ b/src/output_docbook.cpp
@@ -754,7 +754,7 @@ DocBookDocumentSectioning hasDocumentSectioning(ParagraphList const &paragraphs,
 	bool documentHasSections = false;
 
 	while (bpit < epit) {
-		LASSERT(bpit < paragraphs.size(), return make_tuple(documentHasSections, bpit));
+		LASSERT(static_cast<size_t>(bpit) < paragraphs.size(), return make_tuple(documentHasSections, bpit));
 
 		Layout const &style = paragraphs[bpit].layout();
 		documentHasSections |= isLayoutSectioningOrSimilar(style);