The pointer allocated to the `TransData` was being incorrectly incremented,
causing misalignment and consequently `heap-buffer-overflow`.
Because of this, `TD_NOTCONNECTED` was being set in a strange way that did
not correspond to other types of `TransData`.
The solution is to not increment the `TransData` pointer and set
`TD_NOTCONNECTED` only for "unconnected" segments.
The code was also a bit deduplicated.