### 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)

texture_size.width = texture->get_width();
			texture_size.height = texture->get_height();
		}
		ERR_FAIL_COND(p_hotspot.x < 0 || p_hotspot.y < 0);
		ERR_FAIL_COND(texture_size.width > 256 || texture_size.height > 256);
		ERR_FAIL_COND(p_hotspot.x > texture_size.width || p_hotspot.y > texture_size.height);
		Ref<Image> image = texture->get_image();
		ERR_FAIL_COND(!image.is_valid());
		if (image->is_compressed()) {
			image = image->duplicate(true);
			Error err = image->decompress();
			ERR_FAIL_COND_MSG(err != OK, "Couldn't decompress VRAM-compressed custom mouse cursor image. Switch to a lossless compression mode in the Import dock.");
		}
		
		XcursorImage *cursor_image = XcursorImageCreate(texture_size.width, texture_size.height);
		XcursorUInt image_size = texture_size.width * texture_size.height;
		XcursorDim size = sizeof(XcursorPixel) * image_size;
		cursor_image->version = 1;
		cursor_image->size = size;
		cursor_image->xhot = p_hotspot.x;
		cursor_image->yhot = p_hotspot.y;
		
		cursor_image->pixels = (XcursorPixel *)memalloc(size);
		for (XcursorPixel index = 0; index < image_size; index++) {
			int row_index = floor(index / texture_size.width) + atlas_rect.position.y;
			int column_index = (index % int(texture_size.width)) + atlas_rect.position.x;
			if (atlas_texture.is_valid()) {
				column_index = MIN(column_index, atlas_rect.size.width - 1);
				row_index = MIN(row_index, atlas_rect.size.height - 1);
			}