'No commits in common' is shown on pull request with identical branches under the commit tab

[PotatoesFall]

While the link to commits cannot be clicked, visiting the url with /commits will result in the wrong message, similar to the issue described in:

#14502

• Gitea version (or commit ref): 1.14.3
• Git version: ? not sure
• Operating system: Docker
• Database (use [x]):
  • PostgreSQL
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (https://try.gitea.io/PotatoesFall/TestRepo/pulls/1/commits)

Message shown

No commits in common. 'master' and 'other_branch' have entirely different histories.

Message that (I guess) should be shown

These branches are equal.

Screenshots

I have created #16569 to solve this issue