[#478] morph/client: Try to parse integer as a byte type

Neo node can return integers values where []byte is expected.
To cover such cases, try to parse integers in `BytesFromStackItem`.

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pkg/morph/client/util.go

@@ -48,6 +48,13 @@ func BytesFromStackItem(param stackitem.Item) ([]byte, error) {
 	switch param.Type() {
 	case stackitem.BufferT, stackitem.ByteArrayT:
 		return param.TryBytes()
+	case stackitem.IntegerT:
+		n, err := param.TryInteger()
+		if err != nil {
+			return nil, errors.Wrap(err, "can't parse integer bytes")
+		}
+
+		return n.Bytes(), nil
 	case stackitem.AnyT:
 		if param.Value() == nil {
 			return nil, nil

pkg/morph/client/util_test.go

@@ -74,6 +74,10 @@ func TestBytesFromStackItem(t *testing.T) {
 		val, err := BytesFromStackItem(stringByteItem)
 		require.NoError(t, err)
 		require.Equal(t, stringByteItem.Value().([]byte), val)
+
+		val, err = BytesFromStackItem(intItem)
+		require.NoError(t, err)
+		require.Equal(t, intItem.Value().(*big.Int).Bytes(), val)
 	})
 
 	t.Run("incorrect assert", func(t *testing.T) {