Fixup c7496a11: test emptiness before accessing elements

diff --git a/src/Undo.cpp b/src/Undo.cpp
index c0cf56925eee4c1aa9021b73c0d754d37834c37b..693008268a159b2753359ddfcee1a02954dfaa36 100644 (file)
--- a/src/Undo.cpp
+++ b/src/Undo.cpp
@@ -612,7 +612,9 @@ void Undo::endUndoGroup(CursorData const & cur_after)
 
 bool Undo::activeUndoGroup() const
 {
-       return d->group_level_ > 0 && d->undostack_.top().group_id == d->group_id_;
+       return d->group_level_ > 0
+               && !d->undostack_.empty()
+               && d->undostack_.top().group_id == d->group_id_;
 }