Limit req: rate should be non-zero.

Specifying zero rate caused division by zero when calculating delays.

src/http/modules/ngx_http_limit_req_module.c

diff --git a/src/http/modules/ngx_http_limit_req_module.c b/src/http/modules/ngx_http_limit_req_module.c
index 934292e..90434c9 100644
--- a/src/http/modules/ngx_http_limit_req_module.c
+++ b/src/http/modules/ngx_http_limit_req_module.c
@@ -795,7 +795,7 @@
             }
 
             rate = ngx_atoi(value[i].data + 5, len - 5);
-            if (rate <= NGX_ERROR) {
+            if (rate <= 0) {
                 ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                    "invalid rate \"%V\"", &value[i]);
                 return NGX_CONF_ERROR;