[LyX/master] Prevent Outliner crash due to emptied toc value

[Juergen Spitzmueller]

commit 31146ae8d3c058f33931ba40ad36b6ad9c588195
Author: Juergen Spitzmueller <spitz at lyx.org>
Date:   Sat Dec 4 17:53:03 2021 +0100

    Prevent Outliner crash due to emptied toc value
    
    This might need a more profound fix in the long term, see
    https://marc.info/?l=lyx-devel&m=163588729224679&w=2
---
 src/frontends/qt/TocModel.cpp |    5 +++++
 src/frontends/qt/TocModel.h   |    2 ++
 2 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/src/frontends/qt/TocModel.cpp b/src/frontends/qt/TocModel.cpp
index 16990b8..c0c3dce 100644
--- a/src/frontends/qt/TocModel.cpp
+++ b/src/frontends/qt/TocModel.cpp
@@ -327,6 +327,11 @@ TocItem const TocModels::currentItem(QString const & type,
 	}
 	LASSERT(index.model() == it.value()->model(), return TocItem());
 
+	if (it.value()->empty()) {
+		LYXERR(Debug::GUI, "TocModels::currentItem(): requested toc is empty!");
+		return TocItem();
+	}
+
 	return it.value()->tocItem(index);
 }
 
diff --git a/src/frontends/qt/TocModel.h b/src/frontends/qt/TocModel.h
index 55507a0..ee44761 100644
--- a/src/frontends/qt/TocModel.h
+++ b/src/frontends/qt/TocModel.h
@@ -47,6 +47,8 @@ public:
 	///
 	void clear();
 	///
+	bool empty() { return toc_->empty(); }
+	///
 	QAbstractItemModel * model();
 	///
 	QAbstractItemModel const * model() const;