Add io.Closer guidelines (#29387)

Co-authored-by: Yarden Shoham <git@yardenshoham.com>
(cherry picked from commit ad0a34b492c3d41952ff4648c8bfb7b54c376151)

modules/git/blame.go

@@ -115,6 +115,10 @@ func (r *BlameReader) NextPart() (*BlamePart, error) {
 
 // Close BlameReader - don't run NextPart after invoking that
 func (r *BlameReader) Close() error {
+	if r.bufferedReader == nil {
+		return nil
+	}
+
 	err := <-r.done
 	r.bufferedReader = nil
 	_ = r.reader.Close()

modules/git/repo_base_gogit.go

@@ -88,16 +88,17 @@ func OpenRepository(ctx context.Context, repoPath string) (*Repository, error) {
 }
 
 // Close this repository, in particular close the underlying gogitStorage if this is not nil
-func (repo *Repository) Close() (err error) {
+func (repo *Repository) Close() error {
 	if repo == nil || repo.gogitStorage == nil {
-		return
+		return nil
 	}
 	if err := repo.gogitStorage.Close(); err != nil {
 		gitealog.Error("Error closing storage: %v", err)
 	}
+	repo.gogitStorage = nil
 	repo.LastCommitCache = nil
 	repo.tagCache = nil
-	return
+	return nil
 }
 
 // GoGitRepo gets the go-git repo representation

modules/git/repo_base_nogogit.go

@@ -103,7 +103,7 @@ func (repo *Repository) CatFileBatchCheck(ctx context.Context) (WriteCloserError
 	}
 }
 
-func (repo *Repository) Close() (err error) {
+func (repo *Repository) Close() error {
 	if repo == nil {
 		return nil
 	}
@@ -123,5 +123,5 @@ func (repo *Repository) Close() (err error) {
 	}
 	repo.LastCommitCache = nil
 	repo.tagCache = nil
-	return err
+	return nil
 }