Dataflow analysis is hard, let's go shopping!

Another case where the compiler didn't figure out that the variables
aren't used if they're not set.

Change-Id: I70bfb06c6d86d41a266a087ece971c40cd697ee9
Reviewed-on: https://code.wireshark.org/review/4994
Reviewed-by: Guy Harris <guy@alum.mit.edu>