increase request counter before an upstream cleanup because the cleanup
decreases the counter via ngx_http_finalize_request(r, NGX_DONE),
the bug was introduced in r3050

src/http/ngx_http_upstream.c

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 6f15c04..5186b80 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -363,6 +363,7 @@
     u = r->upstream;
 
     if (u && u->cleanup) {
+        r->main->count++;
         ngx_http_upstream_cleanup(r);
         *u->cleanup = NULL;
     }