### Godot version

4.0.3.stable

### System information

Windows 10/11

### Issue description

I want the player's cursor to change when highlighting pickable Area2Ds; to do this, I have the areas modify the `mouse_default_cursor_shape` property on an external Control when the mouse enters or exits. If another Control appears in front of the Area2D while the mouse is over it, there is a chance that the project will crash.

Nothing prints to the IDE's output on this crash. If running the editor with console, then
```
ERROR: Condition "slot >= slot_max" is true. Returning: nullptr
   at: get_instance (./core/object/object.h:972)
```
will sometimes appear alongside the crash. If it appears, it always appears twice.

When I run a debug build of the editor through WinDbg, WinDbg will catch the following exception:
```
(3b58.2aac): Access violation - code c0000005 (!!! second chance !!!)
godot_windows_editor_x86_64!ObjectDB::get_instance [inlined in godot_windows_editor_x86_64!Viewport::_cleanup_mouseover_colliders+0x6f]:
00007ff6`ac254a1f 488b5310        mov     rdx,qword ptr [rbx+10h] ds:cccccccc`c31c419b=????????????????
```
When using this method, the exception is not random; it always occurs on the first attempt.

### Steps to reproduce

- Open the minimal reproduction project in the editor.
- Run the project.
- Click on the Area2D (you'll want visible collision shapes on).
- A full-screen button will pop up. If the game does not crash at this point, clicking the button will hide it so you can try again. It should crash within a few seconds of mashing.

### Minimal reproduction project

[Crash Test.zip](https://github.com/godotengine/godot/files/12027772/Crash.Test.zip)

return false;
	}
	Transform2D window_ofs;
	window_ofs.set_origin(-gui.subwindow_focused->get_position());
	Ref<InputEvent> ev = p_event->xformed_by(window_ofs);
	gui.subwindow_focused->_window_input(ev);
	return true;
}
void Viewport::_update_mouse_over() {
	
	
	if (is_attached_in_viewport()) {
		
		return;
	}
	if (get_tree()->get_root()->is_embedding_subwindows() || is_sub_viewport()) {
		
		_update_mouse_over(gui.last_mouse_pos);
	} else {
		
		Window *receiving_window = get_tree()->get_root()->gui.windowmanager_window_over;
		if (!receiving_window) {
			return;
		}
		Vector2 pos = DisplayServer::get_singleton()->mouse_get_position() - receiving_window->get_position();
		pos = receiving_window->get_final_transform().affine_inverse().xform(pos);
		receiving_window->_update_mouse_over(pos);
	}
}
void Viewport::_update_mouse_over(Vector2 p_pos) {