[checkpoint_io] gather tensor before unpad it if the tensor is both padded and distributed

[Lemon-412]

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🚨 Issue number

fixed #6167

📝 What does this PR do?

To prevent #6167, gather the tensor before unpad it if the tensor is both padded and distributed.

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[Lemon-412]

request review from @flybird11111 @ver217 .

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request review from @flybird11111 @ver217 .