[CH] Fix group limit first array result offset

[lgbo-ustc]

Backend

CH (ClickHouse)

Bug description

cpp-ch/local-engine/AggregateFunctions/GroupLimitFunctions.cpp:138-145 reads ColumnArray offsets from an empty result column.

insertResultInto calls result_array_offsets.back() before pushing the first offset. A newly created aggregate result column has no offsets yet, so the first output row can access an empty container. The previous offset should be treated as 0 when result_array_offsets.empty().

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