Revert "Init QWidget::data to nullptr"

This reverts commit 58b9250.

Reason for revert: This change was obsoleted by
bcd29a9.

Change-Id: I161dfeb471d23a6fdcbf547c1c559784581a5211
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

Author: marcmutz

src/widgets/kernel/qwidget.h

@@ -781,7 +781,7 @@ protected Q_SLOTS:
     Q_PRIVATE_SLOT(d_func(), void _q_showIfNotHidden())
     Q_PRIVATE_SLOT(d_func(), QWindow *_q_closestWindowHandle())
 
-    QWidgetData *data = nullptr; // init'ed in Private::init(), but let's crash before that
+    QWidgetData *data;
 };
 
 Q_DECLARE_OPERATORS_FOR_FLAGS(QWidget::RenderFlags)