incorrect integer conversion

[rip-nsk]

pattern is

    T ret = static_cast<T>(std::strtoX(arg, &endptr, 0));
    if (endptr == arg) {
      throw std::invalid_argument(msg.str());
    }

issues:

• static_cast hides target value overflow if T shorter than long
• unsigned values greater than signed.max() result in ERANGE
• unparsed suffix ignored - "10x" considered as "10"
• throw std::invalid_argument is actually ignored, because

    try {
      return convert::arg<T>(this->arg);
    } catch (...) {
      return t;
    }