Fix zero handling in refmt transfrom

License: MIT
Signed-off-by: Jakub Sztandera <kubuxu@protocol.ai>

chain/types/bigint.go

@@ -133,6 +133,10 @@ func (bi *BigInt) cborBytes() []byte {
 }
 
 func fromCborBytes(buf []byte) (BigInt, error) {
+	if len(buf) == 0 {
+		return NewInt(0), nil
+	}
+
 	var negative bool
 	switch buf[0] {
 	case 0:

chain/types/bigint_test.go

@@ -7,7 +7,7 @@ import (
 
 func TestBigIntSerializationRoundTrip(t *testing.T) {
 	testValues := []string{
-		"0", "1", "10", "9999", "12345678901234567891234567890123456789012345678901234567890",
+		"0", "1", "10", "-10", "9999", "12345678901234567891234567890123456789012345678901234567890",
 	}
 
 	for _, v := range testValues {
@@ -29,5 +29,6 @@ func TestBigIntSerializationRoundTrip(t *testing.T) {
 		if BigCmp(out, bi) != 0 {
 			t.Fatal("failed to round trip BigInt through cbor")
 		}
+
 	}
 }