avformat/http: pass return code from http_open_cnx_internal() on its failure

Previously, AVERROR(EIO) was returned on failure of
http_open_cnx_internal(). Now the value is passed to upper level, thus
it is possible to distinguish ECONNREFUSED, ETIMEDOUT, ENETUNREACH etc.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/http.c

@@ -250,6 +250,8 @@ redo:
 fail:
     if (s->hd)
         ffurl_closep(&s->hd);
+    if (location_changed < 0)
+        return location_changed;
     return ff_http_averror(s->http_code, AVERROR(EIO));
 }