Fix for KT-10047: java.lang.VerifyError: Bad return type

#KT-10047 Fixed

compiler/testData/codegen/boxMultiFile/kt10047/b.kt

@@ -0,0 +1,11 @@
+package test
+
+open class Actor
+
+abstract public class O2dScriptAction<T : Actor> {
+    protected var owner: T? = null
+        private set
+
+    protected fun calc(): T? = null
+
+}