### 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)

ERR_FAIL_COND(!windows.has(p_window));
	WindowData &wd = windows[p_window];
	if (p_enabled && !window_get_flag(WINDOW_FLAG_BORDERLESS, p_window)) {
		
		Hints hints;
		Atom property;
		hints.flags = 2;
		hints.decorations = 0;
		property = XInternAtom(x11_display, "_MOTIF_WM_HINTS", True);
		if (property != None) {
			XChangeProperty(x11_display, wd.x11_window, property, property, 32, PropModeReplace, (unsigned char *)&hints, 5);
		}
	}
	if (p_enabled) {
		
		_update_size_hints(p_window);
	}
	
	XEvent xev;
	Atom wm_state = XInternAtom(x11_display, "_NET_WM_STATE", False);
	Atom wm_fullscreen = XInternAtom(x11_display, "_NET_WM_STATE_FULLSCREEN", False);
	memset(&xev, 0, sizeof(xev));
	xev.type = ClientMessage;
	xev.xclient.window = wd.x11_window;
	xev.xclient.message_type = wm_state;
	xev.xclient.format = 32;
	xev.xclient.data.l[0] = p_enabled ? _NET_WM_STATE_ADD : _NET_WM_STATE_REMOVE;
	xev.xclient.data.l[1] = wm_fullscreen;
	xev.xclient.data.l[2] = 0;