### 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)

return 0;
					}
			}
		} break;
		case WM_CLOSE: 
		{
			if (windows[window_id].focus_timer_id != 0U) {
				KillTimer(windows[window_id].hWnd, windows[window_id].focus_timer_id);
			}
			_send_window_event(windows[window_id], WINDOW_EVENT_CLOSE_REQUEST);
			return 0; 
		}
		case WM_MOUSELEAVE: {
			if (window_mouseover_id == window_id) {
				old_invalid = true;
				window_mouseover_id = INVALID_WINDOW_ID;
				_send_window_event(windows[window_id], WINDOW_EVENT_MOUSE_EXIT);
			} else if (window_mouseover_id != INVALID_WINDOW_ID && windows.has(window_mouseover_id)) {
				
				
				track_mouse_leave_event(windows[window_mouseover_id].hWnd);
			}
		} break;
		case WM_INPUT: {
			if (mouse_mode != MOUSE_MODE_CAPTURED || !use_raw_input) {
				break;
			}
			UINT dwSize;
			GetRawInputData((HRAWINPUT)lParam, RID_INPUT, nullptr, &dwSize, sizeof(RAWINPUTHEADER));
			LPBYTE lpb = new BYTE[dwSize];