### 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)

wd.no_focus = true;
	}
	if (p_flags & WINDOW_FLAG_MOUSE_PASSTHROUGH_BIT) {
		wd.mpass = true;
	}
	if (p_flags & WINDOW_FLAG_POPUP_BIT) {
		wd.is_popup = true;
	}
	if (p_flags & WINDOW_FLAG_TRANSPARENT_BIT) {
		DWM_BLURBEHIND bb;
		ZeroMemory(&bb, sizeof(bb));
		HRGN hRgn = CreateRectRgn(0, 0, -1, -1);
		bb.dwFlags = DWM_BB_ENABLE | DWM_BB_BLURREGION;
		bb.hRgnBlur = hRgn;
		bb.fEnable = TRUE;
		DwmEnableBlurBehindWindow(wd.hWnd, &bb);
		wd.layered_window = true;
	}
	
	HICON mainwindow_icon = (HICON)SendMessage(windows[MAIN_WINDOW_ID].hWnd, WM_GETICON, ICON_SMALL, 0);
	if (mainwindow_icon) {
		SendMessage(windows[window_id].hWnd, WM_SETICON, ICON_SMALL, (LPARAM)mainwindow_icon);
	}
	mainwindow_icon = (HICON)SendMessage(windows[MAIN_WINDOW_ID].hWnd, WM_GETICON, ICON_BIG, 0);
	if (mainwindow_icon) {
		SendMessage(windows[window_id].hWnd, WM_SETICON, ICON_BIG, (LPARAM)mainwindow_icon);
	}
	return window_id;
}
void DisplayServerWindows::show_window(WindowID p_id) {