- Materialize unit when its value is actually needed.
- Special-case Unit_getInstance return type at codegen. It should be a
proper Unit object instead of a "void"
Two changes here: StackValue.Constant does cast iff value is non-null (if null,
no cast between classes is really needed, as null can be an instance of
anything), and codegen for safe qualified expressions uses correct type for the
expression
#KT-4265 Fixed
Svyatoslav Kuzmich