### 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)

gui.subwindow_over = sw;
						if (!sw->is_input_disabled()) {
							sw->_propagate_window_notification(sw, NOTIFICATION_WM_MOUSE_ENTER);
						}
					}
					if (!sw->is_input_disabled()) {
						sw->_update_mouse_over(sw->get_final_transform().affine_inverse().xform(p_pos - sw->get_position()));
					}
				} else {
					if (gui.subwindow_over) {
						gui.subwindow_over->_mouse_leave_viewport();
						gui.subwindow_over = nullptr;
					}
				}
				return;
			}
		}
		if (gui.subwindow_over) {
			
			gui.subwindow_over->_mouse_leave_viewport();
			gui.subwindow_over = nullptr;
		}
	}
	
	Control *over = gui_find_control(p_pos);
	bool notify_embedded_viewports = false;
	if (over != gui.mouse_over) {
		if (gui.mouse_over) {
			_drop_mouse_over();
		} else {