Prevent Stats Indexer reporting error if repo dir missing (#18870)

Repositories missing their directory should not report an error from the stats
indexer.

Close #18847

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/indexer/stats/db.go

@@ -37,6 +37,9 @@ func (db *DBIndexer) Index(id int64) error {
 
 	gitRepo, err := git.OpenRepositoryCtx(ctx, repo.RepoPath())
 	if err != nil {
+		if err.Error() == "no such file or directory" {
+			return nil
+		}
 		return err
 	}
 	defer gitRepo.Close()