fix segfault if no server_name was defined

src/http/ngx_http_core_module.c

diff --git a/src/http/ngx_http_core_module.c b/src/http/ngx_http_core_module.c
index 462393b..b5f24d9 100644
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -2292,9 +2292,12 @@
             return NGX_CONF_ERROR;
         }
 
+#if (NGX_PCRE)
+        sn->regex = NULL;
+#endif
+        sn->core_srv_conf = conf;
         sn->name.len = conf->server_name.len;
         sn->name.data = conf->server_name.data;
-        sn->core_srv_conf = conf;
     }
 
     ngx_conf_merge_size_value(conf->connection_pool_size,