Fix nil checking on typed interface (#17598)

* Fix nil checking on typed interface

- Partially resoles #17596
- Resolves SA4023 errors.
- Ensure correctly that typed interface are nil.

* Remove unnecessary code

`NewBleveIndexer` will never return nil, even on errors.

* Patch `NewBleveIndexer`

* Fix low-level functions

* Remove deadcode

* Fix GetSession

* Close Elastic search when err isn't nil

* Update elastic_search.go

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

modules/indexer/code/indexer.go

@@ -185,9 +185,6 @@ func Init() {
 
 			rIndexer, populate, err = NewBleveIndexer(setting.Indexer.RepoPath)
 			if err != nil {
-				if rIndexer != nil {
-					rIndexer.Close()
-				}
 				cancel()
 				indexer.Close()
 				close(waitChannel)
@@ -205,9 +202,6 @@ func Init() {
 
 			rIndexer, populate, err = NewElasticSearchIndexer(setting.Indexer.RepoConnStr, setting.Indexer.RepoIndexerName)
 			if err != nil {
-				if rIndexer != nil {
-					rIndexer.Close()
-				}
 				cancel()
 				indexer.Close()
 				close(waitChannel)