fix null terminated string parsing

bool InfeBox::parseNullTerminatedString(

        off64_t *offset, size_t *size, String8 *out) {

    char tmp[256];

    size_t len = 0;

    char tmp;

    Vector<char> buf;

    buf.setCapacity(256);

    off64_t newOffset = *offset;

    off64_t stopOffset = *offset + *size;

    while (newOffset < stopOffset) {

        if (!source()->readAt(newOffset++, &tmp[len], 1)) {

        if (!source()->readAt(newOffset++, &tmp, 1)) {

            return false;

        }

        if (tmp[len] == 0) {

            out->append(tmp, len);

        buf.push_back(tmp);

        if (tmp == 0) {

            out->setTo(buf.array());

            *offset = newOffset;

            *size = stopOffset - newOffset;

            return true;

        }

        if (++len >= sizeof(tmp)) {

            out->append(tmp, len);

            len = 0;

        }

    }

    return false;

}