### 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)

visualInfo = vi_list[i];
				if (pict_format->direct.alphaMask > 0) {
					break;
				}
			}
		}
		XFree(vi_list);
	}
	Colormap colormap = XCreateColormap(x11_display, RootWindow(x11_display, visualInfo.screen), visualInfo.visual, AllocNone);
	XSetWindowAttributes windowAttributes = {};
	windowAttributes.colormap = colormap;
	windowAttributes.background_pixel = 0xFFFFFFFF;
	windowAttributes.border_pixel = 0;
	windowAttributes.event_mask = KeyPressMask | KeyReleaseMask | StructureNotifyMask | ExposureMask;
	unsigned long valuemask = CWBorderPixel | CWColormap | CWEventMask;
	if (OS::get_singleton()->is_layered_allowed()) {
		windowAttributes.background_pixmap = None;
		windowAttributes.background_pixel = 0;
		windowAttributes.border_pixmap = None;
		valuemask |= CWBackPixel;
	}
	WindowID id = window_id_counter++;
	WindowData &wd = windows[id];
	if (p_flags & WINDOW_FLAG_NO_FOCUS_BIT) {
		wd.no_focus = true;
	}
	if (p_flags & WINDOW_FLAG_POPUP_BIT) {
		wd.is_popup = true;
	}