Crash on exit of many package editor windows

[mirh]

Describe the bug
I quit the application (from the "close all windows" right-click button in the task bar IIRC) and I got a crash.

To Reproduce
I don't know really. I had only opened a ME1 file, and then through many "find usages in file" and "go to definition" I had several other windows spawned at the time.
Some minor script editing and saving also happened previously, but I don't think it's related.

Expected behavior
Don't crash

Version information:
6.3 nightly 18/08/2023

Stack trace

InvalidOperationException: Cannot set Visibility to Visible or call Show, ShowDialog, Close or WindowInteropHelper.EnsureHandle while a Window is closing.
   at System.Windows.Window.VerifyNotClosing()
   at System.Windows.Window.InternalClose(Boolean shutdown, Boolean ignoreCancel)
   at LegendaryExplorer.MainWindow.LEXMainWindow.CloseSubWindows() in D:\a\1\s\LegendaryExplorer\LegendaryExplorer\MainWindow\LEXMainWindow.xaml.cs:line 239
   at LegendaryExplorer.MainWindow.LEXMainWindow.MainWindow_Closing(Object sender, CancelEventArgs e) in D:\a\1\s\LegendaryExplorer\LegendaryExplorer\MainWindow\LEXMainWindow.xaml.cs:line 253
   at System.Windows.Window.WmClose()
   at System.Windows.Window.WindowFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at System.Windows.Interop.HwndSource.PublicHooksFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndWrapper.WndProc(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)