Handle error on trace raw download with old builds (DB stored)

## What does this MR do?

Handles error on `raw build trace` download action for old builds (which are stored in DB instead of file).

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

No.

## Why was this MR needed?

At the beginning build traces were stored in database but at some point we moved to store them in files. All trace related actions are aware of this, but not `raw trace download`.

## What are the relevant issue numbers?

Fixes #18900

## Does this MR meet the acceptance criteria?


- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [ ] ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4822