fix: adjust twos complement return value for zero in bigIntToTwosComplement

Author: RaphDal

buffer_test.go

@@ -618,6 +618,11 @@ func TestDecimalColumnShopspring(t *testing.T) {
 			value:         fakeShopspringDecimal{coeff: big.NewInt(12345), exp: -2},
 			expectedBytes: []byte{0x17, 0x02, 0x02, 0x30, 0x39},
 		},
+		{
+			name:          "zero",
+			value:         fakeShopspringDecimal{coeff: big.NewInt(0), exp: 0},
+			expectedBytes: []byte{0x17, 0x00, 0x01, 0x00},
+		},
 		{
 			name:          "positive exponent multiplies coefficient",
 			value:         fakeShopspringDecimal{coeff: big.NewInt(123), exp: 2},

decimal.go

@@ -165,7 +165,7 @@ func bigPow10(exponent int) *big.Int {
 
 func bigIntToTwosComplement(value *big.Int) ([32]byte, uint8, error) {
 	if value.Sign() == 0 {
-		return [32]byte{0}, 32, nil
+		return [32]byte{0}, 31, nil
 	}
 	if value.Sign() > 0 {
 		bytes := value.Bytes()