Fix Dead Store (Dead assignement/Dead increment) warning found by Clang

Change-Id: I0593b659dcd28929cf51a8b1147392f070574c9e
Reviewed-on: https://code.wireshark.org/review/3934
Reviewed-by: Roland Knall <rknall@gmail.com>
Reviewed-by: Evan Huus <eapache@gmail.com>