Fix crash of tst_qaccessibilitylinux when DBus is not available.

Change-Id: I32291e4c6a5b228b42a7ec15f1dbfe4302bd31fa
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>

tests/auto/other/qaccessibilitylinux/tst_qaccessibilitylinux.cpp

@@ -90,6 +90,9 @@ class tst_QAccessibilityLinux : public QObject
 {
     Q_OBJECT
 
+public:
+    tst_QAccessibilityLinux() : m_window(0), root(0), rootApplication(0), mainWindow(0) {}
+
 private slots:
     void initTestCase();