Chores: tweak code order

Signed-off-by: Yuanchun Shen <[email protected]>

Author: yuancu

core/src/main/java/org/opensearch/sql/calcite/CalciteRelNodeVisitor.java

@@ -2137,12 +2137,12 @@ public RelNode visitChart(Chart node, CalcitePlanContext context) {
             SqlStdOperatorTable.LESS_THAN_OR_EQUAL,
             relBuilder.field(ROW_NUM_COL),
             relBuilder.literal(limit));
-    RexNode nullCondition = relBuilder.isNull(colSplitPostJoin);
-    RexNode columnSplitExpr;
     if (!config.useOther) {
       relBuilder.filter(lteCondition);
     }
+    RexNode nullCondition = relBuilder.isNull(colSplitPostJoin);
 
+    RexNode columnSplitExpr;
     if (config.useNull) {
       columnSplitExpr =
           relBuilder.call(