JVM_IR KT-50215 KT-50076 extra test

compiler/testData/codegen/box/checkcastOptimization/kt50215.kt

@@ -0,0 +1,19 @@
+// WITH_RUNTIME
+
+class A {
+    fun foo(x: Int = 32) = "OK"
+}
+
+var result = "failed"
+
+fun whoops(x: Any) {
+    when (x) {
+        is A -> result = x.foo()
+        else -> throw AssertionError()
+    }
+}
+
+fun box(): String {
+    whoops(A())
+    return result
+}