GH-343: Fix ListVector offset buffer not allocated for nested empty arrays

[Yicong-Huang]

What's Changed

Fix offset buffer not allocated for nested empty ListVector/LargeListVector during IPC serialization.

When outer array is empty, nested writers are never invoked, so child list's offset buffer remains unallocated (capacity = 0). This violates Arrow spec which requires offset[0] = 0.

Fix

Apply the same fix to getFieldBuffers() as in exportCDataBuffers(): allocate offset buffer if capacity == 0.

Testing

Added tests for nested empty lists verifying offset buffer allocation and offset[0] = 0.

Closes #343.

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