Bugfix: Do not create a local repo unless `init` is used

When a restic command other than `init` is used with a local repository and the
repository directory does not exist, restic creates the directory structure.
That's an error, only the `init` command should create the dir.

https://github.com/restic/restic/issues/1167
https://github.com/restic/restic/pull/1182
