[CH] Fix flatten nullable inner array row handling

[lgbo-ustc]

Backend

CH (ClickHouse)

Bug description

For Array(Nullable(Array(T))), the code scans all nested elements and returns input_rows_count default nullable rows as soon as it sees one null inner array. This makes unrelated rows null. Example: [[[1], null], [[2]]] should only make the first row null under Spark-style flatten semantics, but the current implementation returns both rows as null.

Gluten version

No response

Spark version

None

Spark configurations

No response

System information

No response

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