LibJS: The global isNaN() should coerce to number before testing NaN

For stricter NaN checking, we'll have to implement Number.isNaN().

Libraries/LibJS/Runtime/GlobalObject.cpp

@@ -21,7 +21,7 @@ GlobalObject::GlobalObject()
     put_native_function("isNaN", [](Object*, Vector<Value> arguments) -> Value {
         if (arguments.size() < 1)
             return js_undefined();
-        return Value(arguments[0].is_nan());
+        return Value(arguments[0].to_number().is_nan());
     });
     put("Math", heap().allocate<MathObject>());
 }