qt: Use QDesktopWidget for screen retrival

src/qt/qt_util.cpp

@@ -16,10 +16,23 @@
  */
 #include <QStringBuilder>
 #include <QStringList>
+#include <QWidget>
+#include <QApplication>
+#if QT_VERSION <= QT_VERSION_CHECK(5, 14, 0)
+#include <QDesktopWidget>
+#endif
 #include "qt_util.hpp"
 
 namespace util
 {
+    QScreen* screenOfWidget(QWidget* widget)
+    {
+#if QT_VERSION <= QT_VERSION_CHECK(5, 14, 0)
+        return QApplication::screens()[QApplication::desktop()->screenNumber(widget) == -1 ? 0 : QApplication::desktop()->screenNumber(widget)];
+#else
+        return widget->screen();
+#endif
+    }
 
     QString DlgFilter(std::initializer_list<QString> extensions, bool last)
     {