arsd png bug

[Joerg Joergonson via Digitalmars-d-learn]

1810:
                case 3:
                        auto arr = data.dup;
                        foreach(i; 0 .. arr.length) {
                                auto prev = i < bpp ? 0 : arr[i - bpp];
                                if (i >= previousLine.length) break;
                                arr[i] += cast(ubyte)
                                        /*std.math.floor*/( cast(int) (prev + 
previousLine[i]) / 2);
                        }


adding
        if (i >= previousLine.length) break;

prevents some crashes and seems to work.