[kwindowconfig] Restore window size wrt better screen

By default the window size is restored with respect to the screen at
0,0; this patch uses the screen under mouse cursor.  It is still not
optimal, as one would have to have a way to query the workspace for
the current screen.  Is there any reasonable way to do that?

src/gui/kwindowconfig.cpp

@@ -10,6 +10,9 @@
 #include <QGuiApplication>
 #include <QScreen>
 #include <QWindow>
+#include <QDebug>
+#include <QCursor>
+#include <QGuiApplication>
 
 static const char s_initialSizePropertyName[] = "_kconfig_initial_size";
 static const char s_initialScreenSizePropertyName[] = "_kconfig_initial_screen_size";
@@ -56,8 +59,7 @@ void KWindowConfig::restoreWindowSize(QWindow *window, const KConfigGroup &confi
         return;
     }
 
-    const QRect desk = window->screen()->geometry();
-
+    const QRect desk = QGuiApplication::screenAt(QCursor::pos())->geometry();
     // Fall back to non-per-screen-arrangement info if it's available but
     // per-screen-arrangement information is not
     const int fallbackWidth = config.readEntry(QStringLiteral("Width %1").arg(desk.width()), window->size().width());