### 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)

ImmSetCandidateWindow(windows[window_id].im_himc, &cf);
			cf.dwStyle = CFS_EXCLUDE;
			cf.rcArea.left = windows[window_id].im_position.x;
			cf.rcArea.right = windows[window_id].im_position.x;
			cf.rcArea.top = windows[window_id].im_position.y;
			cf.rcArea.bottom = windows[window_id].im_position.y;
			ImmSetCandidateWindow(windows[window_id].im_himc, &cf);
			if (windows[window_id].ime_active) {
				SetCaretPos(windows[window_id].im_position.x, windows[window_id].im_position.y);
				OS::get_singleton()->get_main_loop()->notification(MainLoop::NOTIFICATION_OS_IME_UPDATE);
			}
		} break;
		case WM_INPUTLANGCHANGEREQUEST: {
			
		} break;
		case WM_IME_STARTCOMPOSITION: {
			if (windows[window_id].ime_active) {
				windows[window_id].ime_in_progress = true;
				if (key_event_pos > 0) {
					key_event_pos--;
				}
			}
			return 0;
		} break;
		case WM_IME_ENDCOMPOSITION: {
			if (windows[window_id].ime_active) {
				windows[window_id].ime_in_progress = false;
				windows[window_id].ime_suppress_next_keyup = true;
			}
			return 0;