### 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)

windows[window_id].focus_timer_id = 0U;
			}
		} break;
		case WM_SYSKEYUP:
		case WM_KEYUP:
		case WM_SYSKEYDOWN:
		case WM_KEYDOWN: {
			if (wParam == VK_SHIFT) {
				shift_mem = (uMsg == WM_KEYDOWN || uMsg == WM_SYSKEYDOWN);
			}
			if (wParam == VK_CONTROL) {
				control_mem = (uMsg == WM_KEYDOWN || uMsg == WM_SYSKEYDOWN);
			}
			if (wParam == VK_MENU) {
				alt_mem = (uMsg == WM_KEYDOWN || uMsg == WM_SYSKEYDOWN);
				if (lParam & (1 << 24)) {
					gr_mem = alt_mem;
				}
			}
			if (windows[window_id].ime_suppress_next_keyup && (uMsg == WM_KEYUP || uMsg == WM_SYSKEYUP)) {
				windows[window_id].ime_suppress_next_keyup = false;
				break;
			}
			if (windows[window_id].ime_in_progress) {
				break;
			}
			if (mouse_mode == MOUSE_MODE_CAPTURED) {
				
				if (wParam == VK_F4 && alt_mem && (uMsg == WM_KEYDOWN || uMsg == WM_SYSKEYDOWN)) {
					_send_window_event(windows[window_id], WINDOW_EVENT_CLOSE_REQUEST);