### 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)

XVisualInfo visualInfo;
	bool vi_selected = false;
#ifdef GLES3_ENABLED
	if (gl_manager) {
		Error err;
		visualInfo = gl_manager->get_vi(x11_display, err);
		ERR_FAIL_COND_V_MSG(err != OK, INVALID_WINDOW_ID, "Can't acquire visual info from display.");
		vi_selected = true;
	}
#endif
	if (!vi_selected) {
		long visualMask = VisualScreenMask;
		int numberOfVisuals;
		XVisualInfo vInfoTemplate = {};
		vInfoTemplate.screen = DefaultScreen(x11_display);
		XVisualInfo *vi_list = XGetVisualInfo(x11_display, visualMask, &vInfoTemplate, &numberOfVisuals);
		ERR_FAIL_COND_V(!vi_list, INVALID_WINDOW_ID);
		visualInfo = vi_list[0];
		if (OS::get_singleton()->is_layered_allowed()) {
			for (int i = 0; i < numberOfVisuals; i++) {
				XRenderPictFormat *pict_format = XRenderFindVisualFormat(x11_display, vi_list[i].visual);
				if (!pict_format) {
					continue;
				}