Issue Summary

Mentioning a commit hash in a Pull Requests comments should create a link to the commit. If the commit belongs to the current repository - the link is created.
If a commit points to a different repository, it's not saved (although it is linked correctly in a comment preview window before saving).
Commit links:

Preview (commit properly linked to another repository) in comments window:

Environment

Tested in Bitbucket 5.15.x -> 6.4

Steps to Reproduce

1. Create a new Pull Request.
2. Mention a commit from the current repository in a comment and save.
3. Mention a commit referring to another repository in a comment and save.

Expected Results

1. Commit from current repository is linked.
2. Commit from the other repository is linked.

Actual Results

• Commit from current repository is linked.
• Commit from the other repository is not linked.

No errors in the logs.

Workaround

Add a full MarkDown link to the commit , e.g.:

[8dd91d1f6d846ec80045699d7ad1ee85395e22ef](/projects/MY_PROJ/repos/my-repo/commits/8dd91d1f6d846ec80045699d7ad1ee85395e22ef) 

// or

[see this commit](https://BITBUCKET_URL/projects/MY_PROJ/repos/my-repo/commits/8dd91d1f6d846ec80045699d7ad1ee85395e22ef)