Script: buffer overrun protection in direct script usage.

Script: buffer overrun protection in direct script usage.

Following the previous change, this change adds script overrun
protection to direct script evaluation in the proxy, fastcgi, scgi,
uwsgi, grpc proxy, index, and try_files modules.

This change is a modified version of a patch by Maxim Dounin.  The
modifications include ngx_http_proxy_v2_module and hardened size checks.

Signed-off-by: Roman Arutyunyan <arut@nginx.com>
Origin: <https://freenginx.org/hg/nginx/rev/7e4d7feb4c77>