fix segfault: ngx_http_upstream_cleanup() cleans r->cleanup,
the bug had been introduced in r3419

src/http/ngx_http_upstream.c

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 776a3a1..273d357 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -365,8 +365,6 @@
     if (u && u->cleanup) {
         r->main->count++;
         ngx_http_upstream_cleanup(r);
-        *u->cleanup = NULL;
-        u->cleanup = NULL;
     }
 
     u = ngx_pcalloc(r->pool, sizeof(ngx_http_upstream_t));