GH-44918: [Ruby] Fix a bug that empty list is ignored in builder

[kou]

Rationale for this change

Arrow::ListArrayBuilder#append_value with [] must append an empty list as an element. In general, it works but it doesn't work when list item is struct or list. Because Arrow::{List,Struct}ArrayBuilder#append without arguments appends an element. It's for a backward compatibility. But it has a problem for this case.

For example, the following case has this problem:

item_type = Arrow::StructDataType.new([{name: "visible", type: :boolean}])
data_type = Arrow::ListDataType.new(name: "struct", data_type: item_type)
builder = Arrow::ListArrayBuilder.new(data_type)
builder.append_value([])
array = builder.finish
array.to_a # => must be [[]] but [] without this change

What changes are included in this PR?

This should be fixed by GH-44763 but the fix was wrong. This change fixes wrong return if location.

Are these changes tested?

Yes.

Are there any user-facing changes?

Yes.

• GitHub Issue: [Ruby] RecordBatchBuilder doesn't work with list of structs #44918

[github-actions]

⚠️ GitHub issue #44918 has been automatically assigned in GitHub to PR creator.

[kou]

+1

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit 1416f62.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details.