Add BB test for problem fixed with c2ab91d0

compiler/testData/codegen/box/enum/javaEnumValueOf2.kt

@@ -0,0 +1,21 @@
+// TARGET_BACKEND: JVM
+// MODULE: m1
+// FILE: E.java
+public enum E {
+    OK();
+    public static E valueOf(int x) {
+        if (x == 0) return OK;
+        return null;
+    }
+}
+
+// MODULE: m2(m1)
+// FILE: test.kt
+
+fun box(): String {
+    return doIt(E.valueOf(0))
+}
+
+fun doIt(e: E) = when (e) {
+    E.OK -> "OK"
+}