fix divide by zero if max_fails=0

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 d9450c9..2479baa 100644
--- a/src/http/ngx_http_upstream_round_robin.c
+++ b/src/http/ngx_http_upstream_round_robin.c
@@ -645,7 +645,9 @@
         peer->fails++;
         peer->accessed = now;
 
-        peer->current_weight -= peer->weight / peer->max_fails;
+        if (peer->max_fails) {
+            peer->current_weight -= peer->weight / peer->max_fails;
+        }
 
         ngx_log_debug2(NGX_LOG_DEBUG_HTTP, pc->log, 0,
                        "free rr peer failed: %ui %i",