message: Fix check that was precisely backwards. Caught by unit tests!
diff: @@ -639,7 +639,7 @@ public:
  SerialiserFlags flags = SerialiserFlags::NoFlags)
  {
  std::string str;
  - if(IsReading())
  + if(IsWriting())
  str = el;
  Serialise(name, str, flags);
  if(str.length() >= N)
  