Fix potential / zore error while one replica

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/plan/AbstractFragmentParallelPlanner.java

diff --git a/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/plan/AbstractFragmentParallelPlanner.java b/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/plan/AbstractFragmentParallelPlanner.java
index bcc6e83..5e13c30 100644
--- a/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/plan/AbstractFragmentParallelPlanner.java
+++ b/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/plan/AbstractFragmentParallelPlanner.java
@@ -137,6 +137,11 @@
   }
 
   private int getTargetIndex(List<TDataNodeLocation> availableDataNodes) {
+    // if only one node is available, just return 0
+    if (availableDataNodes.size() == 1) {
+      return 0;
+    }
+
     int targetIndex;
     if (ReadConsistencyLevel.STRONG == this.readConsistencyLevel
         || queryContext.getSession() == null) {