CORBA24 — null & void TCs and DynAny

The DynAny chapter says nothing about whether
DynAnyFactory::create_dyn_any_from_type_code is supposed to correctly
handle a TypeCode argument that has a TCKind of either tk_null or tk_void.

I assume these are valid argument TypeCodes that do not result in an
InconsistentTypeCode exception, and the returned DynAny is simply one that
fulfills the basic DynAny interface and has no components. However, it
would be nice to explicitly document the cases for these two TypeCodes,
though, given that they're a little different from other TypeCodes in that
they can't have any associated values.

Clarify with additional text as shown below