### 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_
	Ref<FileAccess> f = FileAccess::open(p_filename, FileAccess::READ);
	ERR_FAIL_COND_MSG(f.is_null(), "Cannot open file with icon '" + p_filename + "'.");
	ICONDIR *icon_dir = (ICONDIR *)memalloc(sizeof(ICONDIR));
	int pos = 0;
	icon_dir->idReserved = f->get_32();
	pos += sizeof(WORD);
	f->seek(pos);
	icon_dir->idType = f->get_32();
	pos += sizeof(WORD);
	f->seek(pos);
	ERR_FAIL_COND_MSG(icon_dir->idType != 1, "Invalid icon file format!");
	icon_dir->idCount = f->get_32();
	pos += sizeof(WORD);
	f->seek(pos);
	icon_dir = (ICONDIR *)memrealloc(icon_dir, sizeof(ICONDIR) - sizeof(ICONDIRENTRY) + icon_dir->idCount * sizeof(ICONDIRENTRY));
	f->get_buffer((uint8_t *)&icon_dir->idEntries[0], icon_dir->idCount * sizeof(ICONDIRENTRY));
	int small_icon_index = -1; 
	int small_icon_cc = 0;
	int big_icon_index = -1; 
	int big_icon_width = 16;
	int big_icon_cc = 0;
	for (int i = 0; i < icon_dir->idCount; i++) {
		int colors = (icon_dir->idEntries[i].bColorCount == 0) ? 32768 : icon_dir->idEntries[i].bColorCount;
		int width = (icon_dir->idEntries[i].bWidth == 0) ? 256 : icon_dir->idEntries[i].bWidth;
		if (width == 16) {
			if (colors >= small_icon_cc) {
				small_icon_index = i;
				small_icon_cc = colors;
			}