http: do not call deferred readcb if readcb is not set

Otherwise evhttp_read_cb can be called with invalid connection state:
    http/read_on_write_error: [forking] [msg] libevent using: kqueue
      FAIL ../test/regress_http.c:4079: assert(req)
      FAIL ../test/regress_http.c:4087: assert(req)[err] evhttp_read_cb: illegal connection state 0

1 files changed, 3 insertions, 1 deletions

diff --git a/http.c b/http.c
index 17d45804..4e114b70 100644
--- a/http.c
+++ b/http.c
@@ -1171,7 +1171,9 @@ static void
 evhttp_deferred_read_cb(struct event_callback *cb, void *data)
 {
 	struct evhttp_connection *evcon = data;
-	evhttp_read_cb(evcon->bufev, evcon);
+	struct bufferevent *bev = evcon->bufev;
+	if (bev->readcb)
+		(bev->readcb)(evcon->bufev, evcon);
 }
 
 static void