Fix crash when comparing HKTypeLambda and RefinedType

Calling HKTypeLambda#member will crash when trying to form a NamedType,
this happened in `compareRefinedSlow` so we now skip it. If this
HKTypeLambda is an eta-expansion it will be handled by `fourthTry`.

Somehow, this only started happening after the last commit, when
running:
> vulpix tests/neg
But it's not deterministic, multiple runs may be necessary.
The crash happened while compiling i1650.scala, but compiling this file
by itself didn't trigger the failure.

Author: smarter

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -413,6 +413,9 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
               // of an `AndType` can lead to a cascade of subtyping checks
               // This twist is needed to make collection/generic/ParFactory.scala compile
               fourthTry(tp1, tp2) || compareRefinedSlow
+            case tp1: HKTypeLambda =>
+              // HKTypeLambdas do not have members.
+              fourthTry(tp1, tp2)
             case _ =>
               compareRefinedSlow || fourthTry(tp1, tp2)
           }