Fix TDECCipher.DecodeRawByteString

[danielmarschall]

The following method does not work:

procedure TFormMain.Button2Click(Sender: TObject);
var
  Cipher: TDECCipher;
  s: RawByteString;
begin
  Cipher := TCipher_Null.Create;
  Cipher.Init('', '', $FF);
  Cipher.Mode := cmECBx;
  s := Cipher.EncodeRawByteString('Hello');
  memo1.Lines.Add(s);
  Cipher.Done;

  Cipher.Init('', '', $FF);
  Cipher.Mode := cmECBx;
  memo1.Lines.Add(Cipher.DecodeRawByteString(s));
  Cipher.Done;
end;

It is correctly encrypted, but the decryption outputs an empty string.

The reason is that DoDecode is called with Size=0, because in TDECCipher.DecodeRawByteString, the size is calculated as Length(result) * ..., but result was set to length 0 before.

In comparison: TDECCipher.DecodeBytes Also sets the length of result to 0, but then sets result, so it gets the correct length again. So everything works with DecodeBytes.

This change fixes the issue and TDECCipher.DecodeRawByteString works with the Null cipher now.

I really wonder why didn't any testcase catch this??? @MHumm Maybe you should check the testcases ... I thought something as simple as TDECCipher.DecodeRawByteString should be checked, but I didn't look further in the testcases yet.

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(Maybe you should also introduce this into the stable branch, because I think this is category showstopper/meltdown?)