### 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)

for (int j = 0; j < dev->num_classes; j++) {
#ifdef TOUCH_ENABLED
			if (dev->classes[j]->type == XITouchClass && ((XITouchClassInfo *)dev->classes[j])->mode == XIDirectTouch) {
				direct_touch = true;
			}
#endif
			if (dev->classes[j]->type == XIValuatorClass) {
				XIValuatorClassInfo *class_info = (XIValuatorClassInfo *)dev->classes[j];
				if (class_info->number == VALUATOR_ABSX && class_info->mode == XIModeAbsolute) {
					resolution_x = class_info->resolution;
					abs_x_min = class_info->min;
					abs_x_max = class_info->max;
					absolute_mode = true;
				} else if (class_info->number == VALUATOR_ABSY && class_info->mode == XIModeAbsolute) {
					resolution_y = class_info->resolution;
					abs_y_min = class_info->min;
					abs_y_max = class_info->max;
					absolute_mode = true;
				} else if (class_info->number == VALUATOR_PRESSURE && class_info->mode == XIModeAbsolute) {
					pressure_min = class_info->min;
					pressure_max = class_info->max;
				} else if (class_info->number == VALUATOR_TILTX && class_info->mode == XIModeAbsolute) {
					tilt_x_min = class_info->min;
					tilt_x_max = class_info->max;
				} else if (class_info->number == VALUATOR_TILTY && class_info->mode == XIModeAbsolute) {
					tilt_y_min = class_info->min;
					tilt_y_max = class_info->max;
				}
			}
		}