### 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)

SubWindow sw = gui.sub_windows.write[i];
			
			Rect2i r = Rect2i(sw.window->get_position(), sw.window->get_size());
			if (!sw.window->get_flag(Window::FLAG_BORDERLESS)) {
				
				int title_height = sw.window->get_theme_constant(SNAME("title_height"));
				Rect2i title_bar = r;
				title_bar.position.y -= title_height;
				title_bar.size.y = title_height;
				if (title_bar.size.y > 0 && title_bar.has_point(mb->get_position())) {
					click_on_window = sw.window;
					int close_h_ofs = sw.window->get_theme_constant(SNAME("close_h_offset"));
					int close_v_ofs = sw.window->get_theme_constant(SNAME("close_v_offset"));
					Ref<Texture2D> close_icon = sw.window->get_theme_icon(SNAME("close"));
					Rect2 close_rect;
					close_rect.position = Vector2(r.position.x + r.size.x - close_h_ofs, r.position.y - close_v_ofs);
					close_rect.size = close_icon->get_size();
					if (gui.subwindow_focused != sw.window) {
						
						_sub_window_grab_focus(sw.window);
					}
					if (close_rect.has_point(mb->get_position())) {
						gui.subwindow_drag = SUB_WINDOW_DRAG_CLOSE;
						gui.subwindow_drag_close_inside = true; 
						gui.subwindow_drag_close_rect = close_rect;
					} else {
						gui.subwindow_drag = SUB_WINDOW_DRAG_MOVE;
					}
					gui.subwindow_drag_from = mb->get_position();
					gui.subwindow_drag_pos = sw.window->get_position();