fix V-DOGE-VUL-013 (#51)

* Add Extract unit test case

* ibft verify header with validator list

consensus/ibft/extra_test.go

@@ -25,6 +25,13 @@ func TestExtraEncoding(t *testing.T) {
 				},
 			},
 		},
+		{
+			data: &IstanbulExtra{
+				Validators:    []types.Address{},
+				Seal:          nil,
+				CommittedSeal: [][]byte{},
+			},
+		},
 	}
 
 	for _, c := range cases {

consensus/ibft/ibft.go

@@ -1248,9 +1248,14 @@ func (i *Ibft) isSealing() bool {
 // verifyHeaderImpl implements the actual header verification logic
 func (i *Ibft) verifyHeaderImpl(snap *Snapshot, parent, header *types.Header) error {
 	// ensure the extra data is correctly formatted
-	if _, err := getIbftExtra(header); err != nil {
+	extract, err := getIbftExtra(header)
+	if err != nil {
 		return err
 	}
+	// ensure validatorset exists in extra data
+	if len(extract.Validators) == 0 {
+		return fmt.Errorf("empty extract validatorset")
+	}
 
 	if hookErr := i.runHook(VerifyHeadersHook, header.Number, header.Nonce); hookErr != nil {
 		return hookErr