cli: print is unclear when a row is empty string

version v0.7.1
src csv:
```
c1,c2
,
"",""
```
load data to online in cluster load_mode, select * result is:
```
------ ------
c1 c2
------ ------
NULL NULL
------ ------

2 rows in set
```
2 rows in set, but seems like just one row.

The offline print sytle is more clear:
```
+----+----+
| c1| c2|
+----+----+
|null|null|
| | |
+----+----+
```

Look at the CLI output formatting code, likely in a module handling result display. Compare offline and online print styles to understand the discrepancy. The fix involves adjusting the formatting logic to properly display empty string rows in the online cluster load_mode. Test by loading the provided CSV and verifying the output shows two distinct rows.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.