### 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)

_send_window_event(windows[window_mouseover_id], WINDOW_EVENT_MOUSE_EXIT);
					}
					if (over_id != INVALID_WINDOW_ID && windows.has(over_id)) {
						_send_window_event(windows[over_id], WINDOW_EVENT_MOUSE_ENTER);
					}
				}
				CursorShape c = cursor_shape;
				cursor_shape = CURSOR_MAX;
				cursor_set_shape(c);
				window_mouseover_id = over_id;
				
				track_mouse_leave_event(hWnd);
			}
			
			if (!windows[window_id].window_has_focus && mouse_mode == MOUSE_MODE_CAPTURED) {
				break;
			}
			DisplayServer::WindowID receiving_window_id = _get_focused_window_or_popup();
			if (receiving_window_id == INVALID_WINDOW_ID) {
				receiving_window_id = window_id;
			}
			Ref<InputEventMouseMotion> mm;
			mm.instantiate();
			mm->set_window_id(receiving_window_id);
			mm->set_ctrl_pressed((wParam & MK_CONTROL) != 0);
			mm->set_shift_pressed((wParam & MK_SHIFT) != 0);
			mm->set_alt_pressed(alt_mem);
			if ((tablet_get_current_driver() == "wintab") && wintab_available && windows[window_id].wtctx) {