fix explain analyze file num

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/fragment/FragmentInstanceContext.java

diff --git a/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/fragment/FragmentInstanceContext.java b/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/fragment/FragmentInstanceContext.java
index 67b36a6..62aa75f 100644
--- a/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/fragment/FragmentInstanceContext.java
+++ b/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/fragment/FragmentInstanceContext.java
@@ -820,6 +820,7 @@
 
       this.sharedQueryDataSource =
           new QueryDataSource(Collections.emptyList(), externalTsFileResources);
+      closedUnseqFileNum = externalTsFileResources.size();
       return true;
     } finally {
       addInitQueryDataSourceCost(System.nanoTime() - startTime);