Deleting branch could delete broken branch which has database record but git branch is missing (#35360)

For some reasons, branches between database and git are not synced. If a
branch exists in database but not in the git, it should be able to be
deleted.

---------

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

services/repository/branch.go

@@ -532,8 +532,8 @@ func DeleteBranch(ctx context.Context, doer *user_model.User, repo *repo_model.R
 	// database branch record not exist or it's a deleted branch
 	notExist := git_model.IsErrBranchNotExist(err) || rawBranch.IsDeleted
 
-	commit, err := gitRepo.GetBranchCommit(branchName)
-	if err != nil {
+	branchCommit, err := gitRepo.GetBranchCommit(branchName)
+	if err != nil && !errors.Is(err, util.ErrNotExist) {
 		return err
 	}
 
@@ -549,6 +549,9 @@ func DeleteBranch(ctx context.Context, doer *user_model.User, repo *repo_model.R
 				return fmt.Errorf("DeleteBranch: %v", err)
 			}
 		}
+		if branchCommit == nil {
+			return nil
+		}
 
 		return gitRepo.DeleteBranch(branchName, git.DeleteBranchOptions{
 			Force: true,
@@ -557,20 +560,24 @@ func DeleteBranch(ctx context.Context, doer *user_model.User, repo *repo_model.R
 		return err
 	}
 
-	objectFormat := git.ObjectFormatFromName(repo.ObjectFormatName)
+	if branchCommit == nil {
+		return nil
+	}
 
 	// Don't return error below this
+
+	objectFormat := git.ObjectFormatFromName(repo.ObjectFormatName)
 	if err := PushUpdate(
 		&repo_module.PushUpdateOptions{
 			RefFullName:  git.RefNameFromBranch(branchName),
-			OldCommitID:  commit.ID.String(),
+			OldCommitID:  branchCommit.ID.String(),
 			NewCommitID:  objectFormat.EmptyObjectID().String(),
 			PusherID:     doer.ID,
 			PusherName:   doer.Name,
 			RepoUserName: repo.OwnerName,
 			RepoName:     repo.Name,
 		}); err != nil {
-		log.Error("Update: %v", err)
+		log.Error("PushUpdateOptions: %v", err)
 	}
 
 	return nil