Minor, add regression test

#KT-42554

compiler/testData/codegen/box/coroutines/kt42554.kt

@@ -0,0 +1,21 @@
+// WITH_RUNTIME
+
+import kotlin.coroutines.*
+
+fun launch(block: suspend () -> String): String {
+    var result = ""
+    block.startCoroutine(Continuation(EmptyCoroutineContext) { result = it.getOrThrow() })
+    return result
+}
+
+enum class E { A }
+
+class C(val e: E) {
+    val result = launch {
+        when (e) {
+            E.A -> "OK"
+        }
+    }
+}
+
+fun box(): String = C(E.A).result