Smart cast impossible on when subject is no more recorded #KT-10061 Fixed

compiler/testData/diagnostics/tests/smartCasts/whenSubjectImpossible.kt

@@ -0,0 +1,10 @@
+// See KT-10061
+
+class My {
+    val x: Int? get() = 42
+}
+
+fun foo(my: My) {
+    my.x!!
+    when (my.x) { }
+}