QDockWidget: Fix memory leak when dragging a tab outside of a floating tab window

A QDockWidgetItem will be leaked if a QDockWidget is dragged out of a
floating tab window, and then plugged back somewhere.

The problem is that QMainWindowLayout::unplug was not returning the
QDockWidgetItem* from the floating tab's layout. When that's the case,
a new QDockWidgetItem is created in QDockWidgetPrivate::startDrag
and will be put into the layout, leaking the old QDockWidgetItem.

Change-Id: Ifb9c1c562cb74383ebff1df0f91ee225c5cdb296
Reviewed-by: Sérgio Martins <sergio.martins@kdab.com>
(cherry picked from commit 4d3781b640e8fb0a04e96b2d05199247556b8d86)

1 files changed, 2 insertions, 1 deletions

diff --git a/src/widgets/widgets/qmainwindowlayout.cpp b/src/widgets/widgets/qmainwindowlayout.cpp
index 929a649942..e40e2d4036 100644
--- a/src/widgets/widgets/qmainwindowlayout.cpp
+++ b/src/widgets/widgets/qmainwindowlayout.cpp
@@ -2293,7 +2293,8 @@ QLayoutItem *QMainWindowLayout::unplug(QWidget *widget, bool group)
             // We are unplugging a dock widget from a floating window.
             if (QDockWidget *dw = qobject_cast<QDockWidget*>(widget)) {
                 dw->d_func()->unplug(widget->geometry());
-                return 0;
+                int index = widget->parentWidget()->layout()->indexOf(widget);
+                return widget->parentWidget()->layout()->itemAt(index);
             }
         }
     }