[BUG]When view commit detail it returns 500

[L0veSunshine]

• Gitea version (or commit ref):1.13.0+dev-183-gbc4f7ba69
• Git version:
• Operating system:
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
  • Not relevant
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL) https://try.gitea.io/sakalabid77/CaraMerawatAlatLab/commit/0c57fe15ce3a806afb1730fb9ed551cb0866bf4f,
    https://try.gitea.io/matze1128/Virus_Programm_Matthias/commit/ad2488328cbc7bae3cc1ab184fa422f77bdef205
    ...
  • No
  • Not relevant
• Log gist:

Description

After my test. I suspect this issue may be caused by this pr (#11847).
This issue is same to #11868
Please have a review.

Screenshots

[mrsdizzie]

This is
2020/06/12 12:27:54 ...uters/repo/commit.go:317:Diff() [E] commit.GetTagName: exit status 128 - fatal: No names found, cannot describe anything.

From #11846