idl2wrs (DCERPC DRSUAPI): Fix Dead Store (Dead assignement/Dead increment) warning found by Clang

Add a check if the struct is not empty

budb and butc are also regenerate but no change

Change-Id: I0d8cfc827f5451f1cdbd924628a263af9d483a7b
Reviewed-on: https://code.wireshark.org/review/4473
Reviewed-by: Evan Huus <eapache@gmail.com>