[hotfix][table/runtime] Remove redundant state access in LinkedMultiSetState.add

Author: rkhachatryan

flink-table/flink-table-runtime/src/main/java/org/apache/flink/table/runtime/sequencedmultisetstate/linked/LinkedMultiSetState.java

@@ -154,7 +154,7 @@ public StateChangeInfo<RowData> add(RowData row, long timestamp) throws Exceptio
         final Long highSqn = highSqnAndSize == null ? null : highSqnAndSize.highSqn;
         final long oldSize = highSqnAndSize == null ? 0 : highSqnAndSize.size;
         final RowSqnInfo rowSqnInfo = rowToSqnState.get(key);
-        final Long rowSqn = rowSqnInfo == null ? null : rowToSqnState.get(key).firstSqn;
+        final Long rowSqn = rowSqnInfo == null ? null : rowSqnInfo.firstSqn;
         final boolean isNewRowKey = rowSqn == null; // it's a 1st such record 'row'
         final boolean isNewContextKey = highSqn == null; // 1st a record for current context key