### 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)

#include "display_server_x11.h"
#ifdef X11_ENABLED
#include "x11/detect_prime_x11.h"
#include "x11/key_mapping_x11.h"
#include "core/config/project_settings.h"
#include "core/math/math_funcs.h"
#include "core/string/print_string.h"
#include "core/string/ustring.h"
#include "main/main.h"
#include "scene/resources/texture.h"
#if defined(VULKAN_ENABLED)
#include "servers/rendering/renderer_rd/renderer_compositor_rd.h"
#endif
#if defined(GLES3_ENABLED)
#include "drivers/gles3/rasterizer_gles3.h"
#endif
#include <dlfcn.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>