CidFromReader wraps valid io.EOF in ErrInvalidCid

[gammazero]

When reading from an io.Reader that has no data, the io.EOF error should not be wrapped in ErrInvalidCid. This is not an invalid CID, and is not the same as a partial read which is indicated by io.ErrUnexpectedEOF.

This is an issue because existing code that uses CidFromReader may check for the end of an input stream by if err == io.EOF instead of the preferred if errors.Is(err, io.EOF), and that code will break at runtime after upgrading to go-cid v0.4.0.

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