Update BasicAuthenticationHandler.cs

Hi,

I was having an issue with the Web Api and AllowAnonymous. It is explained in detail [here] (http://stackoverflow.com/questions/15953291/webapidoodle-basicauthenticationhandler-and-webapi-4-not-allowing-anonymous/15956342?noredirect=1#15956342).

The change it to invoke the Web Api. I believe it is safe.