Error on FullScreenHelper.ResetScreenCache when vertical panel location changed

[rozputnii]

Object reference not set to an instance of an object.

at ManagedShell.AppBar.FullScreenHelper.ResetScreenCache() in ManagedShell.AppBar\FullScreenHelper.cs:line 129
at ManagedShell.AppBar.FullScreenHelper.NotifyScreensChanged() in ManagedShell.AppBar\FullScreenHelper.cs:line 134
at ManagedShell.AppBar.AppBarWindow.SetScreenProperties(ScreenSetupReason reason) in ManagedShell.AppBar\AppBarWindow.cs:line 634
at ManagedShell.AppBar.AppBarWindow.ProcessScreenChange(ScreenSetupReason reason) in ManagedShell.AppBar\AppBarWindow.cs:line 534
at ManagedShell.AppBar.AppBarWindow.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) in ManagedShell.AppBar\AppBarWindow.cs:line 456
at System.Windows.Interop.HwndSource.PublicHooksFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)

[rozputnii]

Error reproduced only in .net 8

[dremin]

Fixed by #123.