Fix TCP/UDP/SCTP conversations broken by g59ef97d and g31ecdf5

Bug: 10336
Change-Id: Ia0dbe3abfade59a1c9714eacd8a854eafa6cf879
Reviewed-on: https://code.wireshark.org/review/3379
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>