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: Martin Storsjö <martin@martin.st>

libavformat/http.c

@@ -248,6 +248,8 @@ fail:
     if (s->hd)
         ffurl_close(s->hd);
     s->hd = NULL;
+    if (location_changed < 0)
+        return location_changed;
     return AVERROR(EIO);
 }