QStackedLayout::setCurrentIndex() may crash with very dynamic GUIs

The method QStackedLayout::setCurrentIndex() does the following

1. Store the window's focusWidget() in a local variable
2. hide the old widget
3. show the new widget
4. try to set a sensible new focus widget

When a widget creates its internal structure in its showEvent() and tears down some internal widgets in the hideEvent(), it can happen that the old focus widget is destroyed in step 2 and step 4 uses a dangling pointer.

Solution: Use a QPointer instead:

--- qstackedlayout.cpp.old      2011-03-21 08:10:35.117951000 +0100
+++ qstackedlayout.cpp  2011-03-21 07:57:43.263064000 +0100
@@ -301,7 +301,7 @@
         parent->setUpdatesEnabled(false);
     }

-    QWidget *fw = parent ? parent->window()->focusWidget() : 0;
+    QPointer<QWidget> fw = parent ? parent->window()->focusWidget() : 0;
     if (prev) {
         prev->clearFocus();
         if (d->stackingMode == StackOne)