Cleanup 2

Author: GrigoriyPA

ydb/library/yql/dq/runtime/dq_arrow_helpers.cpp

@@ -1002,8 +1002,10 @@ class TBlockSplitter : public IBlockSplitter {
         }
 
         TItem PopBack(ui64 length) {
-            std::vector<arrow::Datum> backData = Data;
+            MKQL_ENSURE(length <= NumberRows, "Can not pop more than number of rows");
             const auto offset = NumberRows - length;
+
+            std::vector<arrow::Datum> backData = Data;
             for (ui64 i : ArraysIdx) {
                 const auto& array = *Data[i].array();
                 Data[i] = arrow::Datum(array.Slice(0, offset));