[bugfix] Fix nil ptr exception on creating user without running server first (#4094)

# Description

> If this is a code change, please include a summary of what you've coded, and link to the issue(s) it closes/implements.
>
> If this is a documentation change, please briefly describe what you've changed and why.

closes https://codeberg.org/superseriousbusiness/gotosocial/issues/4049 by removing the silly defer statement. Adds a test too, and a warning in the docs.

## Checklist

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- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [x] I/we have commented the added code, particularly in hard-to-understand areas.
- [x] I/we have made any necessary changes to documentation.
- [x] I/we have added tests that cover new code.
- [x] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4094
Co-authored-by: tobi <tobi.smethurst@protonmail.com>
Co-committed-by: tobi <tobi.smethurst@protonmail.com>

docs/admin/cli.md

@@ -57,6 +57,9 @@ Contains `account`, `export`, `import`, and `media` subcommands.
 
 This command can be used to create a new account on your instance.
 
+!!! Warning
+    You must have launched the server at least once before running this command, to initialize essential entries in the database.
+
 `gotosocial admin account create --help`:
 
 ```text