JS: fix support of throwable constructors without message and/or cause parameters

js/js.libraries/src/core/builtins.kt

@@ -61,7 +61,7 @@ internal fun captureStack(baseClass: JsClass<in Throwable>, instance: Throwable)
 @JsName("newThrowable")
 internal fun newThrowable(message: String?, cause: Throwable?): Throwable {
     val throwable = js("new Error()")
-    throwable.message = message
+    throwable.message = if (jsTypeOf(message) == "undefined" && cause != null) cause.toString() else message
     throwable.cause = cause
     return throwable
 }