QSystemTrayIcon: initialize all members

The 'showArrow' member was not init'ed.

Initialize it to true, which is the default value of the
QBalloonTip::showBalloon() function's argument of the same
purpose.

Reported as new by Coverity, but dating back all the way to
cc3875c2e4, so affects all
current branches.

Coverity-Id: 171482
Change-Id: Ica519ecda3a4ae413f606faab8c22f7072f412a8
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

src/widgets/util/qsystemtrayicon.cpp

@@ -436,7 +436,10 @@ bool QBalloonTip::isBalloonVisible()
 
 QBalloonTip::QBalloonTip(QSystemTrayIcon::MessageIcon icon, const QString& title,
                          const QString& message, QSystemTrayIcon *ti)
-    : QWidget(0, Qt::ToolTip), trayIcon(ti), timerId(-1)
+    : QWidget(0, Qt::ToolTip),
+      trayIcon(ti),
+      timerId(-1),
+      showArrow(true)
 {
     setAttribute(Qt::WA_DeleteOnClose);
     QObject::connect(ti, SIGNAL(destroyed()), this, SLOT(close()));