ctx.top_layer_id() keeps returning the same layer id after closing or not drawing a window

[OwlyCode]

Describe the bug
When a window is closed, ctx.top_layer_id() keeps returning its layer id.

To Reproduce
Steps to reproduce the behavior:

1. Open a window
2. Call ctx.top_layer_id()
3. Close the window (using the .open() method or by not drawing it at all)
4. Call ctx.top_layer_id() again, it's the same layer id.

Expected behavior
I'd have expected it to return None if no more window are opened or the layer id of the next windows that gets on top.

Desktop (please complete the following information):

• OS: Windows 11

Additional context
I tested a change that would fix it here: d3aacc5

Ready to PR that if needed!