### 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)

mb->set_button_index(MouseButton::MB_XBUTTON1);
					} else {
						mb->set_button_index(MouseButton::MB_XBUTTON2);
					}
				} break;
				case WM_XBUTTONDBLCLK: {
					mb->set_pressed(true);
					if (HIWORD(wParam) == XBUTTON1) {
						mb->set_button_index(MouseButton::MB_XBUTTON1);
					} else {
						mb->set_button_index(MouseButton::MB_XBUTTON2);
					}
					mb->set_double_click(true);
				} break;
				default: {
					return 0;
				}
			}
			mb->set_ctrl_pressed((wParam & MK_CONTROL) != 0);
			mb->set_shift_pressed((wParam & MK_SHIFT) != 0);
			mb->set_alt_pressed(alt_mem);
			
			if (mb->is_pressed()) {
				last_button_state.set_flag(mouse_button_to_mask(mb->get_button_index()));
			} else {
				last_button_state.clear_flag(mouse_button_to_mask(mb->get_button_index()));
			}
			mb->set_button_mask(last_button_state);
			mb->set_position(Vector2(GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam)));
			if (mouse_mode == MOUSE_MODE_CAPTURED && !use_raw_input) {