Fix uninitializing fields when evaluating a cached constructor call

[Cherry-picked a722358]

Author: EnzeXing

Diff for: compiler/src/dotty/tools/dotc/transform/init/Objects.scala

@@ -950,7 +950,6 @@ class Objects(using Context @constructorOnly):
 
         val instance = OfClass(klass, outerWidened, ctor, args.map(_.value), envWidened)
         callConstructor(instance, ctor, args)
-        instance
 
     case ValueSet(values) =>
       values.map(ref => instantiate(ref, klass, ctor, args)).join

Diff for: tests/init-global/pos/cache-constructor.scala

@@ -0,0 +1,9 @@
+class Bar:
+    var f: Int = 0
+
+object A:
+    val b1 = new Bar()
+    val b2 = new Bar()
+    val b3 = new Bar()
+    b3.f = 1
+