JS: when RHS of as cast is non-nullable native interface, check LHS for null

js/js.translator/testData/box/native/safeCastToNativeInterface.kt

@@ -0,0 +1,9 @@
+@native interface I {
+    fun foo(): String
+}
+fun createObject(): Any? = null
+
+fun box(): String {
+    val result = (createObject() as? I)?.foo()
+    return if (result == null) "OK" else "fail"
+}