### 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)

const WindowData &wd = windows[window_id];
				bool focused = wd.focused;
				if (mouse_mode == MOUSE_MODE_CAPTURED) {
					if (xi.relative_motion.x == 0 && xi.relative_motion.y == 0) {
						break;
					}
					Point2i new_center = pos;
					pos = last_mouse_pos + xi.relative_motion;
					center = new_center;
					do_mouse_warp = focused; 
				}
				if (!last_mouse_pos_valid) {
					last_mouse_pos = pos;
					last_mouse_pos_valid = true;
				}
				
				
				
				
				
				
				Point2i rel;
				
				if (mouse_mode == MOUSE_MODE_CAPTURED) {
					rel = xi.relative_motion;
				} else {
					rel = pos - last_mouse_pos;
				}
				
				xi.relative_motion.x = 0;