### 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 (gui.subwindow_drag != SUB_WINDOW_DRAG_DISABLED) {
		ERR_FAIL_COND_V(gui.currently_dragged_subwindow == nullptr, false);
		Ref<InputEventMouseButton> mb = p_event;
		if (mb.is_valid() && !mb->is_pressed() && mb->get_button_index() == MouseButton::LEFT) {
			if (gui.subwindow_drag == SUB_WINDOW_DRAG_CLOSE) {
				if (gui.subwindow_drag_close_rect.has_point(mb->get_position())) {
					
					gui.currently_dragged_subwindow->_event_callback(DisplayServer::WINDOW_EVENT_CLOSE_REQUEST);
				}
			}
			gui.subwindow_drag = SUB_WINDOW_DRAG_DISABLED;
			if (gui.currently_dragged_subwindow != nullptr) { 
				_sub_window_update(gui.currently_dragged_subwindow);
				gui.currently_dragged_subwindow = nullptr;
			}
		}
		Ref<InputEventMouseMotion> mm = p_event;
		if (mm.is_valid()) {
			if (gui.subwindow_drag == SUB_WINDOW_DRAG_MOVE) {
				Vector2 diff = mm->get_position() - gui.subwindow_drag_from;
				Rect2i new_rect(gui.subwindow_drag_pos + diff, gui.currently_dragged_subwindow->get_size());
				if (gui.currently_dragged_subwindow->is_clamped_to_embedder()) {
					new_rect = gui.currently_dragged_subwindow->fit_rect_in_parent(new_rect, get_visible_rect());