user32: Return reasonable values in GetWindowPlacement for the desktop window.

dlls/user32/winpos.c

@@ -1172,7 +1172,20 @@ BOOL WINAPI GetWindowPlacement( HWND hwnd, WINDOWPLACEMENT *wndpl )
 {
     WND *pWnd = WIN_GetPtr( hwnd );
 
-    if (!pWnd || pWnd == WND_DESKTOP) return FALSE;
+    if (!pWnd) return FALSE;
+
+    if (pWnd == WND_DESKTOP)
+    {
+        wndpl->length  = sizeof(*wndpl);
+        wndpl->showCmd = SW_SHOWNORMAL;
+        wndpl->flags = 0;
+        wndpl->ptMinPosition.x = -1;
+        wndpl->ptMinPosition.y = -1;
+        wndpl->ptMaxPosition.x = -1;
+        wndpl->ptMaxPosition.y = -1;
+        GetWindowRect( hwnd, &wndpl->rcNormalPosition );
+        return TRUE;
+    }
     if (pWnd == WND_OTHER_PROCESS)
     {
         if (IsWindow( hwnd )) FIXME( "not supported on other process window %p\n", hwnd );