[LyX/master] Fix computation of InsetCollapsible's button dimension

[Jean-Marc Lasgouttes]

commit ba4682bd2860b08438b467c11c3f86b123976c15
Author: Jean-Marc Lasgouttes <lasgouttes at lyx.org>
Date:   Sun Jun 21 16:41:09 2026 +0200

    Fix computation of InsetCollapsible's button dimension
    
    Fixes bug #13311.
---
 src/insets/InsetCollapsible.cpp | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/insets/InsetCollapsible.cpp b/src/insets/InsetCollapsible.cpp
index 14ea0a9825..699d6172ea 100644
--- a/src/insets/InsetCollapsible.cpp
+++ b/src/insets/InsetCollapsible.cpp
@@ -257,9 +257,8 @@ void InsetCollapsible::metrics(MetricsInfo & mi, Dimension & dim) const
 			view_[&bv].openinlined_ = (textdim.wid + dim.wid) < mi.base.textwidth;
 			if (view_[&bv].openinlined_) {
 				// Correct for button width but remove spacing before frame
-				dim.wid += textdim.wid - leftOffset(mi.base.bv) / 2;
-				dim.des = max(dim.des - textdim.asc + dim.asc, textdim.des);
-				dim.asc = textdim.asc;
+				dim += textdim;
+				dim.wid -= leftOffset(mi.base.bv) / 2;
 			} else {
 				dim.des += textdim.height() + topOffset(mi.base.bv);
 				dim.wid = max(dim.wid, textdim.wid);