QGraphicsProxyWidget: Don't crash within setWidget() when a child proxy has no assigned widget

QGraphicsProxyWidget::setWidget() is checking if the newly assigned
widget is already assigned to a child proxy widget without checking if
the child has a widget assigned at all which lead to a nullptr reference
if it is not the case.
Therefore check if the assigned widget is a valid pointer.

Fixes: QTBUG-15442
Change-Id: I006877f99895ca01975bdcad071cfcf90bea22ad
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/widgets/graphicsview/qgraphicsproxywidget.cpp b/src/widgets/graphicsview/qgraphicsproxywidget.cpp
index 177dbc4871..513cf9d361 100644
--- a/src/widgets/graphicsview/qgraphicsproxywidget.cpp
+++ b/src/widgets/graphicsview/qgraphicsproxywidget.cpp
@@ -607,20 +607,20 @@ void QGraphicsProxyWidgetPrivate::setWidget_helper(QWidget *newWidget, bool auto
         for (QGraphicsItem *child : childItems) {
             if (child->d_ptr->isProxyWidget()) {
                 QGraphicsProxyWidget *childProxy = static_cast<QGraphicsProxyWidget *>(child);
-                QWidget * parent = childProxy->widget();
-                while (parent->parentWidget() != 0) {
+                QWidget *parent = childProxy->widget();
+                while (parent && parent->parentWidget()) {
                     if (parent == widget)
                         break;
                     parent = parent->parentWidget();
                 }
                 if (!childProxy->widget() || parent != widget)
                     continue;
-                childProxy->setWidget(0);
+                childProxy->setWidget(nullptr);
                 delete childProxy;
             }
         }
 
-        widget = 0;
+        widget = nullptr;
 #ifndef QT_NO_CURSOR
         q->unsetCursor();
 #endif