Fix links to old commits in merge request comments

What does this MR do?

It makes sure hash is always returned in version_params

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

nil can be returned from version_params_for method and we use this value then in version_params. We assume that it is always hash in https://gitlab.com/gitlab-org/gitlab-ce/blob/a794b161cd996f3328c0b9a60d0e3cbdaee2a914/app/models/diff_discussion.rb#L26 . But when it is nil an error is raised.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?

Closes #41492 (closed)