During subtyping/incorporation we transform types (e.g. changing nullability,
form of the type) and, basically, we're doing this to some FIXPOINT.
It's important that we use `KotlinType.hashCode()` to compare types, but
for error types hashCode is a hashCode of its supertype and, for example,
`makeNullableAsSpecified` method recreate type every time. So, we continue
to generate new constraints and we'll never stop incorporation algorithm
Previously, there was receiver of type Nothing, which could case result
of the call to be inferred to Nothing too. This could case bogus
UNREACHABLE_CODE diagnostics in cases like this:
```
fun <T> id(x: T) = x
fun test() {
id(unresolvedReference) // type of statement is 'Nothing'
// ... everything here is marked as unreachable ...
}
```
This commit changes type of receiver for such calls form Nothing to
ErrorType.
Mikhail Zarechenskiy