### 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)

ERR_READ_THREAD_GUARD_V(nullptr);
	return camera_3d;
}
void Viewport::_camera_3d_transform_changed_notify() {
}
void Viewport::_camera_3d_set(Camera3D *p_camera) {
	if (camera_3d == p_camera) {
		return;
	}
	if (camera_3d) {
		camera_3d->notification(Camera3D::NOTIFICATION_LOST_CURRENT);
	}
	camera_3d = p_camera;
	if (!camera_3d_override) {
		if (camera_3d) {
			RenderingServer::get_singleton()->viewport_attach_camera(viewport, camera_3d->get_camera());
		} else {
			RenderingServer::get_singleton()->viewport_attach_camera(viewport, RID());
		}
	}
	if (camera_3d) {
		camera_3d->notification(Camera3D::NOTIFICATION_BECAME_CURRENT);
	}
	_update_audio_listener_3d();
	_camera_3d_transform_changed_notify();
}
bool Viewport::_camera_3d_add(Camera3D *p_camera) {