OCSP stapling: fixed ssl_stapling_file (ticket #769).

Broken by 6893a1007a7c (1.9.2) during introduction of strict OCSP response
validity checks.  As stapling file is expected to be returned unconditionally,
fix is to set its validity to the maximum supported time.

Reported by Faidon Liambotis.

src/event/ngx_event_openssl_stapling.c

@@ -245,6 +245,7 @@ ngx_ssl_stapling_file(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_str_t *file)
 
     staple->staple.data = buf;
     staple->staple.len = len;
+    staple->valid = NGX_MAX_TIME_T_VALUE;
 
     return NGX_OK;