### 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)

XClientMessageEvent m;
					memset(&m, 0, sizeof(m));
					m.type = ClientMessage;
					m.display = event.xclient.display;
					m.window = event.xclient.data.l[0];
					m.message_type = xdnd_status;
					m.format = 32;
					m.data.l[0] = windows[window_id].x11_window;
					m.data.l[1] = (requested != None);
					m.data.l[2] = 0; 
					m.data.l[3] = 0;
					m.data.l[4] = xdnd_action_copy;
					XSendEvent(x11_display, event.xclient.data.l[0], False, NoEventMask, (XEvent *)&m);
					XFlush(x11_display);
				} else if ((unsigned int)event.xclient.message_type == (unsigned int)xdnd_drop) {
					if (requested != None) {
						xdnd_source_window = event.xclient.data.l[0];
						if (xdnd_version >= 1) {
							XConvertSelection(x11_display, xdnd_selection, requested, XInternAtom(x11_display, "PRIMARY", 0), windows[window_id].x11_window, event.xclient.data.l[2]);
						} else {
							XConvertSelection(x11_display, xdnd_selection, requested, XInternAtom(x11_display, "PRIMARY", 0), windows[window_id].x11_window, CurrentTime);
						}
					} else {
						
						XClientMessageEvent m;
						memset(&m, 0, sizeof(m));
						m.type = ClientMessage;
						m.display = event.xclient.display;
						m.window = event.xclient.data.l[0];