Always try to fetch repo for mirrors (go-gitea#19975)

- Always give a best-effort to fetching the repositories, if even that
fails indeed give a disconnected mirror found error.
- *Partially* resolves go-gitea#19928

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/mirror/mirror.go

@@ -63,7 +63,7 @@ func Update(ctx context.Context, pullLimit, pushLimit int) error {
 		var item SyncRequest
 		var repo *repo_model.Repository
 		if m, ok := bean.(*repo_model.Mirror); ok {
-			if m.Repo == nil {
+			if m.GetRepository() == nil {
 				log.Error("Disconnected mirror found: %d", m.ID)
 				return nil
 			}
@@ -73,7 +73,7 @@ func Update(ctx context.Context, pullLimit, pushLimit int) error {
 				ReferenceID: m.RepoID,
 			}
 		} else if m, ok := bean.(*repo_model.PushMirror); ok {
-			if m.Repo == nil {
+			if m.GetRepository() == nil {
 				log.Error("Disconnected push-mirror found: %d", m.ID)
 				return nil
 			}