findClass / accessClass throw unexpected exceptions

There are several issues with MethodHandles.Lookup.findClass() and accessClass() after JEP 274 was integrated:

1. accessClass() doesn't throw IAE on lookup object when a private static nested class of the other class is passed as an argument;

2. the same problem with findClass();

3. findClass() throws ClassNotFoundException on publicLookup object when a private static nested class of the other class is passed as an argument.