process: check env->EmitProcessEnvWarning() last

Calling env->EmitProcessEnvWarning() prevents additional warnings
from being set it should therefore be called only if a warning will
emit.

PR-URL: https://github.com/nodejs/node/pull/25575


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>