[BugFix] generate statistics for empty iceberg table

[hongli-my]

What type of PR is this：

• [x] bug
• [ ] feature
• [ ] enhancement
• [ ] refactor
• [ ] others

Which issues of this PR fixes ：

Fixes #6840

Problem Summary(Required) ：

return statistics for empty iceberg table, and record is zero.

[hongli-my]

@DorianZheng , plz review it.

I want to add ut, maybe add in generate optimizedPlan, but how to contruct iceberg table.

[imay]

@hongli-my you can rerun the job just left a message like "run starrocks_fe_unittest", then the job will run atomaticly

[wanpengfei-git]

[FE PR Coverage check]

:disappointed: fail : 0 / 17 (00.00%)

file detail

	path	covered line	new line	coverage
:large_blue_circle:	com/starrocks/external/iceberg/cost/IcebergTableStatisticCalculator.java	0	17	00.00%

[hongli-my]

run starrocks_fe_unittest

[DorianZheng]

run starrocks_fe_unittest

[hongli-my]

plz add ut

done, I mock currentSnapshot function to return null to generate IcebergFileStats

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

0.0% Coverage
0.0% Duplication

[wanpengfei-git]

[FE PR Coverage Check]

:disappointed: fail : 1 / 17 (05.88%)

file detail

	path	covered_line	new_line	coverage	not_covered_line_detail
:large_blue_circle:	com/starrocks/external/iceberg/cost/IcebergTableStatisticCalculator.java	1	17	05.88%	[70, 71, 72, 74, 75, 76, 77, 78, 79, 80, 81, 84, 85, 86, 225, 226]

[wangruin]

run starrocks_admit_test

[wanpengfei-git]

run starrocks_admit_test

[Youngwb]

@Mergifyio backport branch-2.4

[mergify[bot]]

backport branch-2.4

✅ Backports have been created

• #11352 [BugFix] generate statistics for empty iceberg table (backport #6846) has been created for branch branch-2.4