Bug description

If the parent class has private members, then when serializing the child class I get the exeption "to access field 'xxx' failed".

This happens in two cases:

1. The parent and child classes are in different assemblies.
2. The child class has no members.
   2.1 If there are two child classes. One with fields and the other without. Then it matters in what order I try to serialize them. If I serialize the class with fields first, then the class without fields will also be successfully serialized. But if I serialize the class without fields first, then there will be an error.

• Version used: 3,1,3
• Runtime: 8,0

Additional context

https://github.com/LavrinenkoRuslan/TestMessagePack