config: Make --list and --get work on empty repos

The --list and --get implementations work just fine
on empty repos (reporting the default values). So
don't err out prematurely during option parsing.

Closes: #2585
Approved by: alexlarsson
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f