message: Fix copy-paste bug
  Summary: Write correct code. Fixes GitHub issue
diff: @@ -208,8 +208,8 @@ class TaggedBase {
  // See copy constructor. Assignment operators for lint.
  ValueStream& operator=(const ValueStream&) { not_reached(); }
  ValueStream& operator=(ValueStream&& rhs) {
  - oss(std::move(rhs.oss));
  - trg(rhs.trg);
  + oss = std::move(rhs.oss);
  + trg = rhs.trg;
  rhs.disposed = true;
  return *this;
  }
  