remove duplicate offset=0

Backported to master-1,12 from master

Change-Id: I6653b733dfd2c587909371e50fd0c2efc4649dcd
Reviewed-on: https://code.wireshark.org/review/2482
Reviewed-by: Martin Kaiser <wireshark@kaiser.cx>
Reviewed-on: https://code.wireshark.org/review/3003
Reviewed-by: Bill Meier <wmeier@newsguy.com>