Start the "callback register ID" at 1, so that zeroed out callback IDs
are not found during unregister.
Change-Id: I1d7d70f53d89c40e07d1637e1e195dd027855ed3
Reviewed-on: https://code.wireshark.org/review/20385
Reviewed-by: Michael Mann <mmann78@netscape.net>
Petri-Dish: Michael Mann <mmann78@netscape.net>
Reviewed-by: Evan Huus <eapache@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>