smartcontract: fix wildcard trusts deserialization

If manifest trusts presented as Null stackitem, then they should be
treated as wildcard, not as restricted.

It's not the same problem as described and fixed in
https://github.com/neo-project/neo/pull/2901 and
https://github.com/neo-project/neo/pull/2892, although these
two PRs are related.

Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>

pkg/core/state/contract_test.go

@@ -55,6 +55,16 @@ func TestContractStateToFromSI(t *testing.T) {
 	t.Run("Convertible", func(t *testing.T) {
 		contractDecoded := new(Contract)
 		testserdes.ToFromStackItem(t, contract, contractDecoded)
+
+		t.Run("preserve wildcard trusts", func(t *testing.T) {
+			contract.Manifest.Trusts.Value = nil
+			require.True(t, contract.Manifest.Trusts.IsWildcard())
+			actual := new(Contract)
+			item, err := contract.ToStackItem()
+			require.NoError(t, err)
+			require.NoError(t, actual.FromStackItem(item))
+			require.True(t, actual.Manifest.Trusts.IsWildcard())
+		})
 	})
 	t.Run("JSON", func(t *testing.T) {
 		contractDecoded := new(Contract)

pkg/smartcontract/manifest/manifest.go

@@ -250,7 +250,7 @@ func (m *Manifest) FromStackItem(item stackitem.Item) error {
 		m.Permissions[i] = *p
 	}
 	if _, ok := str[6].(stackitem.Null); ok {
-		m.Trusts.Restrict()
+		m.Trusts = WildPermissionDescs{Value: nil} // wildcard by default
 	} else {
 		if str[6].Type() != stackitem.ArrayT {
 			return errors.New("invalid Trusts stackitem type")