make `show stats` work when only one file changed (#32244)
fix https://github.com/go-gitea/gitea/issues/32226
in https://github.com/go-gitea/gitea/pull/27775 , it do some changes to
only show diff file tree when more than one file changed. But looks it
also break the `diff-file-list` logic, which looks not expected change.
so try fix it.
/cc @silverwind
example view:
![image](https://github.com/user-attachments/assets/
281e9c4f-a269-4d36-94eb-
a132058aea87)
Signed-off-by: a1012112796 <1012112796@qq.com>