Support uploading file to empty repo by API (#24357)

The uploading API already works (the only nit is the the IsEmpty flag is
out-of-sync, this PR also fixes it)

Close #14633

services/repository/files/update.go

@@ -458,6 +458,11 @@ func CreateOrUpdateRepoFile(ctx context.Context, repo *repo_model.Repository, do
 	if err != nil {
 		return nil, err
 	}
+
+	if repo.IsEmpty {
+		_ = repo_model.UpdateRepositoryCols(ctx, &repo_model.Repository{ID: repo.ID, IsEmpty: false}, "is_empty")
+	}
+
 	return file, nil
 }