fix(network): populate ChaincodeInput.Args in fsc test proposal helper

fabric-smart-client v0.15.1's transaction.UnpackProposal now rejects a
ChaincodeInvocationSpec with an empty Input.Args slice. The fsc endorsement
tests' newValidProposalBytes helper built proposals with an empty
ChaincodeInput, which proposalKey's replay-key extraction unpacks on every
call, so every responder test in the package failed.

Signed-off-by: Angelo De Caro <adc@zurich.ibm.com>

Author: adecaro

token/services/network/fabric/endorsement/fsc/responder_test.go

@@ -85,7 +85,7 @@ func newValidProposalBytes(t *testing.T, txID string, creator, nonce []byte, tim
 	cis := &pb.ChaincodeInvocationSpec{
 		ChaincodeSpec: &pb.ChaincodeSpec{
 			ChaincodeId: &pb.ChaincodeID{Name: "a_namespace", Version: "1.0"},
-			Input:       &pb.ChaincodeInput{},
+			Input:       &pb.ChaincodeInput{Args: [][]byte{[]byte("invoke")}},
 		},
 	}
 	proposalPayload := &pb.ChaincodeProposalPayload{