Snippet repo: Remove safe navigators and return early

The following discussion from !205897 (merged) should be addressed:

• @jwoodwardgl started a discussion: (+1 comment)

  nitpick(non-blocking) you've already verified that snippet exists so the extra safe navigator is unnecessary

      self.organization = snippet.organization if snippet&.organization_id.present?
      self.project = snippet.project if snippet&.project_id.present?

  In fact, we can actually just return early if there's no snippet and remove all safe navigators

      return if compact_sharding_keys.size == 1 || snippet.nil?
  
      self.organization = snippet.organization if snippet.organization_id.present?
      self.project = snippet.project if snippet.project_id.present?