Fix SSE-C source decryption handling (#6671)
Fix SSE-C source decryption handling (#6671)

Without this fix we have room for two different type of
errors.
- Source is encrypted and we didn't provide any source encryption keys

This results in Incomplete body error to be returned back to the client
since source is encrypted and we gave the reader as is to the object
layer which was of a decrypted value leading to "IncompleteBody"

- Source is not encrypted and we provided source encryption keys.

This results in a corrupted object on the destination which is
considered encrypted but cannot be read by the server and returns
the following error.

```
<Error><Code>XMinioObjectTampered</Code><Message>The requested object
was modified and may be compromised</Message><Resource>/id-platform-gamma/
</Resource><RequestId>155EDC3E86BFD4DA</RequestId><HostId>3L137</HostId>
</Error>
```
aead/minio,balamurugana/minio,jimjag/minio,fwessels/minio,jimjag/minio,aead/minio,minio/minio,aead/minio,minio/minio,jimjag/minio,harshavardhana/minio,harshavardhana/minio,NitishT/minio,NitishT/minio,krishnasrinivas/minio,harshavardhana/minio,fwessels/minio,vadmeste/minio,krishnasrinivas/minio,krisis/minio,vadmeste/minio,harshavardhana/minio,donatello/minio,aead/minio,donatello/minio,NitishT/minio,harshavardhana/minio,krishnasrinivas/minio,aead/minio,NitishT/minio,harshavardhana/minio,krishnasrinivas/minio,fwessels/minio,fwessels/minio,aead/minio,harshavardhana/minio,jimjag/minio,aead/minio,aead/minio,krisis/minio,harshavardhana/minio,balamurugana/minio