fix success determination when protocol != http(s)

When protocol != http(s) (i.e. file:// or any custom. I use ufs:// in my custom qtwebkit application) reqwest will handle it like an error, but these protocols cannot set xhr.status, so it is a case when we have the data in xhr.response, we have xhr.readyState == 4, but xhr.status == 0

So I added the check for protocol and if it http(s) then use your old check, else we will see if xhr.response if truthy