Fix doubled elastic index in alias after error

Author: VaD1ke

app/code/Magento/Elasticsearch/Model/Adapter/Elasticsearch.php

@@ -193,6 +193,9 @@ public function addDocs(array $documents, $storeId, $mappedIndexerId)
      */
     public function cleanIndex($storeId, $mappedIndexerId)
     {
+        // needed to fix bug with double indices in alias because of second reindex in same process
+        unset($this->preparedIndex[$storeId]);
+
         $this->checkIndex($storeId, $mappedIndexerId, true);
         $indexName = $this->indexNameResolver->getIndexName($storeId, $mappedIndexerId, $this->preparedIndex);
         if ($this->client->isEmptyIndex($indexName)) {