ECC decoding can be done with any encoded.K blocks, and now we start it once any K blocks arrived.
Previous code essentially waited for all blocks to arrive (or fail to arrive), that may mean unnecessary delays.
New code will sometimes ECC-decode when parity blocks were retrieved faster that data blocks (instead of waiting for data blocks from network), but we expect that it's OK due to extremely fast Leopard decoding (~~500 MB/s)
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