Make sure widening does not refer non-existent abstract objects

Author: liufengyun

compiler/src/dotty/tools/dotc/transform/init/Semantic.scala

@@ -351,10 +351,8 @@ class Semantic {
         case addr: Addr =>
           // widen the outer to finitize addresses
           val outer = addr match
-            case _: ThisRef => addr
-            case warm: Warm =>
-              if warm.outer.isInstanceOf[Warm] then warm.copy(outer = Cold)
-              else warm
+            case Warm(_, _: Warm) => Cold
+            case _ => addr
 
           val value = Warm(klass, outer)
           if !heap.contains(value) then

tests/init/neg/inner-loop.scala

@@ -1,6 +1,6 @@
 class Outer { outer =>
   class Inner extends Outer {
-    val x = 5 + outer.n
+    val x = 5 + outer.n    // error
   }
   val inner = new Inner
   val n = 6               // error