Backport #28334 by @lng2020
Fix#28328
```
func (p *PullRequestComment) GetDiffHunk() string {
if p == nil || p.DiffHunk == nil {
return ""
}
return *p.DiffHunk
}
```
This function in the package `go-github` may return an empty diff. When
it's empty, the following code will panic because it access `ss[1]`
ec1feedbf5/services/migrations/gitea_uploader.go (L861-L867)ec1feedbf5/modules/git/diff.go (L97-L101)
Co-authored-by: Nanguan Lin <70063547+lng2020@users.noreply.github.com>
(cherry picked from commit 8b590de186)
693c2b4f15