Using an unsupported CursorType causes a crash

[Miron Alexandru]

The following code causes a segmentation fault on Debian 12. This is due to CSFML's sfCursor_createFromSystem returning a null pointer for unsupported cursors, and C#'s cursor taking that pointer and using it as-is.

using SFML.Window;

namespace SFMLRepro;

public static class Program
{
    public static void Main(string[] args)
    {
        using var window = new Window(new VideoMode(1280, 720), "SFML Cursor Crash");
        
        var cursorType = Cursor.CursorType.ArrowWait;
        
        using var cursor = new Cursor(cursorType);
        window.SetMouseCursor(cursor);
    }
}

I'd expect there to be an exception explaining the issue instead of the application hard crashing from this, since the C++ lib returns booleans to communicate success or failure of the operation. I think there's other places in the code that might have a similar issue (like the other constructor that calls sfCursor_createFromPixels and also takes the pointer as-is).