QzTools: Use correct screen for widget in centerWidgetOnScreen

BUG: 384543

src/lib/tools/qztools.cpp

@@ -1,6 +1,6 @@
 /* ============================================================
 * Falkon - Qt web browser
-* Copyright (C) 2010-2017 David Rosca <nowrep@gmail.com>
+* Copyright (C) 2010-2018 David Rosca <nowrep@gmail.com>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
@@ -110,7 +110,7 @@ QByteArray QzTools::readAllFileByteContents(const QString &filename)
 
 void QzTools::centerWidgetOnScreen(QWidget* w)
 {
-    const QRect screen = QApplication::desktop()->screenGeometry();
+    const QRect screen = QApplication::desktop()->screenGeometry(w);
     const QRect size = w->geometry();
     w->move((screen.width() - size.width()) / 2, (screen.height() - size.height()) / 2);
 }