message: fix a crash issue when copying a RequestFailedException with null RawResponse
diff: @@ -102,7 +102,10 @@ namespace Azure { namespace Core {
  : std::runtime_error(other.Message), StatusCode(other.StatusCode),
  ReasonPhrase(other.ReasonPhrase), ClientRequestId(other.ClientRequestId),
  RequestId(other.RequestId), ErrorCode(other.ErrorCode), Message(other.Message),
  - RawResponse(std::make_unique<Azure::Core::Http::RawResponse>(*other.RawResponse))
  + RawResponse(
  + other.RawResponse
  + ? std::make_unique<Azure::Core::Http::RawResponse>(*other.RawResponse)
  + : nullptr)
  {
  }
  