Fix for KT-14597: "When" over smartcasted enum is broken and breaks all other "when"

#KT-14597 Fixed

compiler/testData/codegen/box/when/enumOptimization/kt14597.kt

@@ -0,0 +1,22 @@
+enum class En { A, B, С }
+
+fun box(): String {
+    var res = ""
+    // nullable variable
+    val en2: Any? = En.A
+    if (en2 is En) {
+        when (en2) {
+            En.A -> {res += "O"}
+            En.B -> {}
+            En.С -> {}
+        }
+
+        when (en2 as En) {
+            En.A -> {res += "K"}
+            En.B -> {}
+            En.С -> {}
+        }
+    }
+
+    return res
+}