Overridable val should not be treated as constant

#KT-9443 fixed

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/MiscTest.java

@@ -56,6 +56,10 @@ public final class MiscTest extends AbstractExpressionTest {
         checkOutput("KT-1052.kt", "true\n");
     }
 
+    public void testKt9443() throws Exception {
+        checkFooBoxIsOk("kt9443.kt");
+    }
+
     public void testKt740_1() throws Exception {
         checkFooBoxIsTrue("KT-740.kt");
     }

js/js.translator/testData/expression/misc/cases/kt9443.kt

@@ -0,0 +1,20 @@
+package foo
+
+abstract class BaseClass {
+    protected open val menuId: Int = 0
+
+    public fun run(): Pair<String, Boolean> =
+            "$menuId" to (menuId == 0)
+}
+
+class ImplClass: BaseClass() {
+    override val menuId: Int = 3
+}
+
+public fun box(): String {
+    val result = ImplClass().run()
+
+    if (result != ("3" to false)) return "Fail: $result"
+
+    return "OK"
+}