Follow-up from "Fix force-routing to Gitaly primary with empty hook env"

The following discussion from !54317 (merged) should be addressed:

• @dbalexandre started a discussion:

  We can use #blank? to check if the object is not nil or empty and remove the guard clause above.

        return {} unless Gitlab::SafeRequestStore.active?
        return {} if Gitlab::SafeRequestStore[:gitlab_git_env].blank?