FAB-2368 check for transaction action existence

https://jira.hyperledger.org/browse/FAB-2368

Got a panic from an unchecked access to transaction action
array.  This happened because the SDK client was out of sync on
protos, but still, this should be handled gracefully.

Change-Id: I8e2d1ed0fbd6ebba2baf11bc87dfaeb529fcc8f4
Signed-off-by: Srinivasan Muralidharan <[email protected]>

Author: Srinivasan Muralidharan

protos/utils/proputils.go

@@ -469,6 +469,10 @@ func GetActionFromEnvelope(envBytes []byte) (*peer.ChaincodeAction, error) {
 		return nil, err
 	}
 
+	if len(tx.Actions) == 0 {
+		return nil, fmt.Errorf("At least one TransactionAction is required")
+	}
+
 	_, respPayload, err := GetPayloads(tx.Actions[0])
 	return respPayload, err
 }