Fixed crash when encountering invalid forms.

Crash when replacing the QDockWidget contents
widget by a widget using a container extension.

Task-number: 254553

1 files changed, 4 insertions, 1 deletions

diff --git a/tools/designer/src/components/formeditor/formwindow.cpp b/tools/designer/src/components/formeditor/formwindow.cpp
index 07d785afcb..66bab9b34d 100644
--- a/tools/designer/src/components/formeditor/formwindow.cpp
+++ b/tools/designer/src/components/formeditor/formwindow.cpp
@@ -2136,7 +2136,10 @@ void FormWindow::layoutContainer(QWidget *w, int type)
 bool FormWindow::hasInsertedChildren(QWidget *widget) const // ### move
 {
     if (QDesignerContainerExtension *container = qt_extension<QDesignerContainerExtension*>(core()->extensionManager(), widget)) {
-        widget = container->widget(container->currentIndex());
+        const int index = container->currentIndex();
+        if (index < 0)
+            return false;
+        widget = container->widget(index);
     }
 
     const QWidgetList l = widgets(widget);