No assignee
Access the issue list page and select `No assignee`, you will get 500 error:  You can see this page in try.gitea.io: https://try.gitea.io/yp05327/testrepo/issues?q=&type=all&sort=&state=open&labels=&milestone=0&project=0&assignee=-1&poster=0 Caused by https://github.com/go-gitea/gitea/pull/24707/files#diff-d7c7dc2da4fcfdc09997648e11a018414dc116472054350b5590ab407adcd44dR1748 Co-authored-by: Giteabot <teabot@gitea.io>
This PR - [x] Move some functions from `issues.go` to `issue_stats.go` and `issue_label.go` - [x] Remove duplicated issue options `UserIssueStatsOption` to keep only one `IssuesOptions`