--retry: access violation with URL part sets continued

When getting multiple URLs, curl didn't properly reset the byte counter
after a successful transfer so if the subsequent transfer failed it
would wrongly use the previous byte counter and behave badly (segfault)
because of that. The code assumes that the byte counter and the 'stream'
pointer is well in synch.

Reported by: Jon Sargeant
Bug: http://curl.haxx.se/bug/view.cgi?id=3028241