syslog: fix PID of forking process

Do not cache PID for a process that does not fabricate it,
calls openlog() before forking and does not call exec() thereafter.

PR: 268666
Fixes: e9ae9fa93745669b7dd0341d333257ad6cfe8e37
Tested by: kp

(cherry picked from commit 2ce3ef55035093cac7839e71e9ff91f5562ebc29)