progresscallback: make CURLE_ABORTED_BY_CALLBACK get returned better

When the progress callback returned 1 at a very early state, the code
would not make CURLE_ABORTED_BY_CALLBACK get returned but the process
would still be interrupted. In the HTTP case, this would then cause a
CURLE_GOT_NOTHING to erroneously get returned instead.

Reported-by: Petr Novak
Bug: http://curl.haxx.se/bug/view.cgi?id=1318