Avoid orphan RefinedThis types in glb/lub.

Author: odersky

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

@@ -929,7 +929,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
           tp1.derivedRefinedType(
               tp1.parent & tp2.parent,
               tp1.refinedName,
-              tp1.refinedInfo & tp2.refinedInfo)
+              tp1.refinedInfo & tp2.refinedInfo.substRefinedThis(tp2, RefinedThis(tp1)))
         case _ =>
           NoType
       }
@@ -995,7 +995,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
           tp1.derivedRefinedType(
               tp1.parent | tp2.parent,
               tp1.refinedName,
-              tp1.refinedInfo | tp2.refinedInfo)
+              tp1.refinedInfo | tp2.refinedInfo.substRefinedThis(tp2, RefinedThis(tp1)))
         case _ =>
           NoType
       }

src/dotty/tools/dotc/core/tasty/TreePickler.scala

@@ -201,7 +201,7 @@ class TreePickler(pickler: TastyPickler) {
       case tpe: RefinedThis =>
         writeByte(REFINEDthis)
         val binderAddr = pickledTypes.get(tpe.binder)
-        assert(binderAddr != null)
+        assert(binderAddr != null, tpe.binder)
         writeRef(binderAddr.asInstanceOf[Addr])
       case tpe: SkolemType =>
         pickleType(tpe.info)