### 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)

if (!viewport_under) {
					
					viewport_under = embedder;
				}
			} else {
				
				Vector2i screen_mouse_pos = DisplayServer::get_singleton()->mouse_get_position();
				DisplayServer::WindowID window_id = DisplayServer::get_singleton()->get_window_at_screen_position(screen_mouse_pos);
				if (window_id != DisplayServer::INVALID_WINDOW_ID) {
					ObjectID object_under = DisplayServer::get_singleton()->window_get_attached_instance_id(window_id);
					if (object_under != ObjectID()) { 
						Window *w = Object::cast_to<Window>(ObjectDB::get_instance(object_under));
						if (w) {
							viewport_under = w;
							viewport_pos = screen_mouse_pos - w->get_position();
						}
					}
				}
			}
			if (viewport_under) {
				if (viewport_under != this) {
					Transform2D ai = viewport_under->get_final_transform().affine_inverse();
					viewport_pos = ai.xform(viewport_pos);
				}
				
				gui.drag_mouse_over = viewport_under->gui_find_control(viewport_pos);
				if (gui.drag_mouse_over) {
					Transform2D localizer = gui.drag_mouse_over->get_global_transform_with_canvas().affine_inverse();
					gui.drag_mouse_over_pos = localizer.xform(viewport_pos);
					bool can_drop = _gui_drop(gui.drag_mouse_over, gui.drag_mouse_over_pos, true);