fix-encoding-args.pl: Fix bug: certain patterns found only in 1st,3rd,... file checked

  Another perl "You can't DO that" ...

Change-Id: I56e11bec19515f883f15286c6aa45018a255ab53
Reviewed-on: https://code.wireshark.org/review/4172
Reviewed-by: Bill Meier <wmeier@newsguy.com>