refactor: In functions like ListOffChainData and GetMissingBatchKeys, although defer rows.Close() is used, if QueryxContext fails, rows will be nil. Calling defer rows.Close() in this case can trigger a panic.

refactor: In functions like ListOffChainData and GetMissingBatchKeys, although defer rows.Close() is used, if QueryxContext fails, rows will be nil. Calling defer rows.Close() in this case can trigger a panic. #596