### 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)

old_x = mm->get_position().x;
					old_y = mm->get_position().y;
					if (windows[window_id].window_has_focus || window_get_active_popup() == window_id) {
						Input::get_singleton()->parse_input_event(mm);
					}
				}
				return 0;
			}
		} break;
		case WM_POINTERENTER: {
			if (mouse_mode == MOUSE_MODE_CAPTURED && use_raw_input) {
				break;
			}
			if ((tablet_get_current_driver() != "winink") || !winink_available) {
				break;
			}
			uint32_t pointer_id = LOWORD(wParam);
			POINTER_INPUT_TYPE pointer_type = PT_POINTER;
			if (!win8p_GetPointerType(pointer_id, &pointer_type)) {
				break;
			}
			if (pointer_type != PT_PEN) {
				break;
			}
			windows[window_id].block_mm = true;
			return 0;
		} break;
		case WM_POINTERLEAVE: {
			windows[window_id].block_mm = false;
			return 0;