(Slim) Packed DateTimeOffset is equal to MinValue after deserialization

```
static readonly SlimSerializer serializer = new SlimSerializer();

static byte[] Serialize(object obj)
{
using (var ms = new MemoryStream())
{
serializer.Serialize(ms, obj);
return ms.ToArray();
}
}
static object Deserialize(byte[] data)
{
using (var ms = new MemoryStream(data))
{
return serializer.Deserialize(ms);
}
}

static void Main(string[] args)
{
var dateTimeOffsetNow = DateTimeOffset.Now;
var packedDateTimeOffset = new {Now = dateTimeOffsetNow};

var serializedDateTimeOffset = Serialize(dateTimeOffsetNow);
var serializedPackedDateTimeOffset = Serialize(packedDateTimeOffset);

var deserializedDateTimeOffsetNow = Deserialize(serializedDateTimeOffset);
var deserializedPackedDateTimeOffset = (dynamic) Deserialize(serializedPackedDateTimeOffset);
}

// dateTimeOffsetNow: 6/27/2019 1:02:12 PM +03:00
// deserializedDateTimeOffsetNow: 6/27/2019 1:02:12 PM +03:00

// packedDateTimeOffset.Now: 6/27/2019 1:02:12 PM +03:00
// deserializedPackedDateTimeOffset.Now: 1/1/0001 12:00:00 AM +00:00
```