BUG: FixedList/Pair writeEntry not re-readable (fixes #2351)

- notably affects writing continuous data in binary. If generating a
  compound token (eg, List<label>), need to add in the size prefix
  otherwise it cannot actually be parsed properly as a List.

BUG: bad fallthrough for compound reading (FixedList)

- the branch was likely never reached, but would have attempted to
  read twice due to a bad fall-through condition.