Missing previous comments when diffing against new commit
### Summary
Comments from a previous commit are not visible when diffing with a new commit
### Steps to reproduce
1. Create a new merge request.
2. Comment on specific lines of the code diff. Comments appear inline with lines of code.
3. Add a commit to the merge request.
4. View the diff between commit 1 and commit 2. Comments for commit 1 do not appear inline with the lines of code.
### Example Project
Comments on commit 1
https://gitlab.com/j-joshua/jjtestproject/merge_requests/1/diffs?commit_id=e9a4b200a57d134da05060a837edf6fe29f986ed
Comments missing when diffing commit 2 and commit 1
https://gitlab.com/j-joshua/jjtestproject/merge_requests/1/diffs?commit_id=56b9e345bc2561cccb5c76cfcd6584175925ec50
### What is the current *bug* behavior?
The diff between commit 1 and commit 2 is displayed without comments inline for commit 1.
### What is the expected *correct* behavior?
Comments appear inline for commit 1.
### Relevant logs and/or screenshots
### Output of checks
#### Results of GitLab environment info
#### Results of GitLab application Check
### Possible fixes
issue