net/pload: fix crash at startup

Looks like there was no NULL pointer at the end of the orig_argv[] when
it was copied or restored.

PR: 274354
Reported by: Rupert Stitzinger <stitzinger_rupert@web.de>
MFH: 2023Q4

(cherry picked from commit ffaf1c4515dd11fc28fd00c97ae5c8ff78aca4e1)