### 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)

title_text.set_direction(p_window->is_layout_rtl() ? TextServer::DIRECTION_RTL : TextServer::DIRECTION_LTR);
		int x = (r.size.width - title_text.get_size().x) / 2;
		int y = (-title_height - title_text.get_size().y) / 2;
		Color font_outline_color = p_window->get_theme_color(SNAME("title_outline_modulate"));
		int outline_size = p_window->get_theme_constant(SNAME("title_outline_size"));
		if (outline_size > 0 && font_outline_color.a > 0) {
			title_text.draw_outline(sw.canvas_item, r.position + Point2(x, y), outline_size, font_outline_color);
		}
		title_text.draw(sw.canvas_item, r.position + Point2(x, y), title_color);
		bool pressed = gui.subwindow_focused == sw.window && gui.subwindow_drag == SUB_WINDOW_DRAG_CLOSE && gui.subwindow_drag_close_inside;
		Ref<Texture2D> close_icon = p_window->get_theme_icon(pressed ? "close_pressed" : "close");
		close_icon->draw(sw.canvas_item, r.position + Vector2(r.size.width - close_h_ofs, -close_v_ofs));
	}
	RS::get_singleton()->canvas_item_add_texture_rect(sw.canvas_item, r, sw.window->get_texture()->get_rid());
}
void Viewport::_sub_window_grab_focus(Window *p_window) {
	if (p_window == nullptr) {
		
		if (gui.subwindow_focused) {
			gui.subwindow_focused->_event_callback(DisplayServer::WINDOW_EVENT_FOCUS_OUT);
			gui.subwindow_focused = nullptr;
			gui.subwindow_drag = SUB_WINDOW_DRAG_DISABLED;
		}
		Window *this_window = Object::cast_to<Window>(this);
		if (this_window) {
			this_window->_event_callback(DisplayServer::WINDOW_EVENT_FOCUS_IN);
		}
		return;
	}