Otherwise accessing rows at `n` will lead to heap buffer overflow
```
5# SipHash::update(char const*, unsigned long) at /home/zcp/repo_center/doris_master/doris/be/src/vec/common/sip_hash.h:132
6# doris::vectorized::ColumnString::update_hash_with_value(unsigned long, SipHash&) const at /home/zcp/repo_center/doris_master/doris/be/src/vec/columns/column_string.h:452
7# doris::vectorized::ColumnObject::update_hash_with_value(unsigned long, SipHash&) const at /home/zcp/repo_center/doris_master/doris/be/src/vec/columns/column_object.cpp:1433
8# doris::vectorized::Block::update_hash(SipHash&) const at /home/zcp/repo_center/doris_master/doris/be/src/vec/core/block.cpp:721
9# doris::EngineChecksumTask::_compute_checksum() at
```