Upstream: fixed unlocked access to peer->conns.

src/http/ngx_http_upstream_round_robin.c

diff --git a/src/http/ngx_http_upstream_round_robin.c b/src/http/ngx_http_upstream_round_robin.c
index 52da545..487b0e3 100644
--- a/src/http/ngx_http_upstream_round_robin.c
+++ b/src/http/ngx_http_upstream_round_robin.c
@@ -599,17 +599,20 @@
 
     peer = rrp->current;
 
+    ngx_http_upstream_rr_peers_rlock(rrp->peers);
+    ngx_http_upstream_rr_peer_lock(rrp->peers, peer);
+
     if (rrp->peers->single) {
 
         peer->conns--;
 
+        ngx_http_upstream_rr_peer_unlock(rrp->peers, peer);
+        ngx_http_upstream_rr_peers_unlock(rrp->peers);
+
         pc->tries = 0;
         return;
     }
 
-    ngx_http_upstream_rr_peers_rlock(rrp->peers);
-    ngx_http_upstream_rr_peer_lock(rrp->peers, peer);
-
     if (state & NGX_PEER_FAILED) {
         now = ngx_time();