### Godot version

Godot Engine v4.0.stable.official.92bee43ad

### System information

Windows 10

### Issue description

The documentation states that passing ```null``` into the image parameter of ```set_custom_mouse_cursor``` will change it back to the system cursor, however I find that it removes the cursor's image entirely, rather than setting it to the system's cursor.


### Steps to reproduce

```var isimage = false
var theimage = load("res://final.png")

func _on_my_button_pressed():
    if isimage == false:
        Input.set_custom_mouse_cursor(theimage, Input.CURSOR_ARROW, Vector2(16,16))
        isimage = true
        
    else:
        Input.set_custom_mouse_cursor(null)
        isimage = false```

When the button is pressed, the cursor is meant to change to the new cursor. When it has been pressed a second time, it changes back to the default cursor. However, upon pressing it a second time, it simply disappears. The cursor becomes visible again when the cursor exits and re-enters the window.

### Minimal reproduction project

[null mouse.zip](https://github.com/godotengine/godot/files/10901969/null.mouse.zip)

wd.parent = RootWindow(x11_display, visualInfo.screen);
		XSetWindowAttributes window_attributes_ime = {};
		window_attributes_ime.event_mask = KeyPressMask | KeyReleaseMask | StructureNotifyMask | ExposureMask;
		wd.x11_xim_window = XCreateWindow(x11_display, wd.x11_window, 0, 0, 1, 1, 0, CopyFromParent, InputOnly, CopyFromParent, CWEventMask, &window_attributes_ime);
#ifdef XKB_ENABLED
		if (dead_tbl && xkb_loaded_v05p) {
			wd.xkb_state = xkb_compose_state_new(dead_tbl, XKB_COMPOSE_STATE_NO_FLAGS);
		}
#endif
		
		
		if (!wd.no_focus && !wd.is_popup) {
			XSelectInput(x11_display, wd.x11_window, StructureNotifyMask);
		}
		
		
		{
			const long pid = OS::get_singleton()->get_process_id();
			Atom net_wm_pid = XInternAtom(x11_display, "_NET_WM_PID", False);
			if (net_wm_pid != None) {
				XChangeProperty(x11_display, wd.x11_window, net_wm_pid, XA_CARDINAL, 32, PropModeReplace, (unsigned char *)&pid, 1);
			}
		}
		long im_event_mask = 0;
		{
			XIEventMask all_event_mask;
			XSetWindowAttributes new_attr;
			new_attr.event_mask = KeyPressMask | KeyReleaseMask | ButtonPressMask |
					ButtonReleaseMask | EnterWindowMask |
					LeaveWindowMask | PointerMotionMask |