[Feature Request] Mandate a final transcoding rule for *

[brian-doherty]

gonic version: 0.20

if from docker, docker tag:
if from source, git tag/branch: c8cc0dd

I recently had a little trouble because I used a new client and it tried to transcode, and I didn't have a rule for that client, or *. I'd like to suggest that the final * rule be mandatory.