[BugFix] Fix comment broken issue ref dependence (#12651)

* deleteIssuesByRepoID: delete related CommentTypeRemoveDependency & CommentTypeAddDependency comments too

* Ignore ErrIssueNotExist on comment.LoadDepIssueDetails()

* Add migration

* Ignore 'dependent_issue_id = 0' case

* exchange as per @lunny

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

models/issue.go

@@ -1978,6 +1978,11 @@ func deleteIssuesByRepoID(sess Engine, repoID int64) (attachmentPaths []string,
 		return
 	}
 
+	if _, err = sess.In("dependent_issue_id", deleteCond).
+		Delete(&Comment{}); err != nil {
+		return
+	}
+
 	var attachments []*Attachment
 	if err = sess.In("issue_id", deleteCond).
 		Find(&attachments); err != nil {