fastcgi: Ensure leading slash, omit SERVER_PORT if empty for compliance (#3570)
fastcgi: Ensure leading slash, omit SERVER_PORT if empty for compliance (#3570)

See https://tools.ietf.org/html/rfc3875#section-4.1.13 for SCRIPT_NAME requiring leading slash
See https://tools.ietf.org/html/rfc3875#section-4.1.15 for SERVER_PORT requiring omission if empty
abiosoft/caddy,mholt/caddy,abiosoft/caddy,l3dlp/caddy,l3dlp/caddy,l3dlp/caddy,mholt/caddy