### 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)

_THREAD_SAFE_METHOD_
	ERR_FAIL_COND(!windows.has(p_window));
	WindowData &wd = windows[p_window];
	WindowMode old_mode = window_get_mode(p_window);
	if (old_mode == p_mode) {
		return; 
	}
	
	switch (old_mode) {
		case WINDOW_MODE_WINDOWED: {
			
		} break;
		case WINDOW_MODE_MINIMIZED: {
			_set_wm_minimized(p_window, false);
		} break;
		case WINDOW_MODE_EXCLUSIVE_FULLSCREEN:
		case WINDOW_MODE_FULLSCREEN: {
			
			wd.fullscreen = false;
			wd.exclusive_fullscreen = false;
			_set_wm_fullscreen(p_window, false, false);
			
			bool on_top = window_get_flag(WINDOW_FLAG_ALWAYS_ON_TOP, p_window);
			window_set_position(wd.last_position_before_fs, p_window);
			if (on_top) {
				_set_wm_maximized(p_window, false);
			}
		} break;
		case WINDOW_MODE_MAXIMIZED: {
			_set_wm_maximized(p_window, false);