AbstractOpenPGPDocumentSignatureGenerator: Properly apply signature c…

[vanitasvitae]

…reation time from SignatureParameters

This fixes OpenPGPMessageGenerator not applying custom signature creation times for message signatures.

        // Generate message at t1
        OpenPGPMessageGenerator mGen = api.signAndOrEncryptMessage()
                .addSigningKey(key, new SignatureParameters.Callback() {
                    @Override
                    public SignatureParameters apply(SignatureParameters parameters) {
                        return parameters.setSignatureCreationTime(t1); // this call was ignored, but is fixed with the patch.
                    }
                });