### 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)

state->set_shift_pressed((p_x11_state & ShiftMask));
	state->set_ctrl_pressed((p_x11_state & ControlMask));
	state->set_alt_pressed((p_x11_state & Mod1Mask )); 
	state->set_meta_pressed((p_x11_state & Mod4Mask));
}
BitField<MouseButtonMask> DisplayServerX11::_get_mouse_button_state(MouseButton p_x11_button, int p_x11_type) {
	MouseButtonMask mask = mouse_button_to_mask(p_x11_button);
	if (p_x11_type == ButtonPress) {
		last_button_state.set_flag(mask);
	} else {
		last_button_state.clear_flag(mask);
	}
	return last_button_state;
}
void DisplayServerX11::_handle_key_event(WindowID p_window, XKeyEvent *p_event, LocalVector<XEvent> &p_events, uint32_t &p_event_index, bool p_echo) {
	WindowData &wd = windows[p_window];
	
	XKeyEvent *xkeyevent = p_event;
	if (wd.ime_in_progress) {
		return;
	}
	if (wd.ime_suppress_next_keyup) {
		wd.ime_suppress_next_keyup = false;
		if (xkeyevent->type != KeyPress) {
			return;