journal: Fix syslog forwarding without CAP_SYS_ADMIN

In case CAP_SYS_ADMIN is missing (like in containers), one cannot fake pid in
struct ucred (uid/gid are fine if CAP_SETUID/CAP_SETGID are present).

Ensure that journald will try again to forward the messages to syslog without
faking the SCM_CREDENTIALS pid (which isn't guaranteed to succeed anyway, since
it also does the same thing if the process has already exited).

With this patch, journald will no longer silently discard messages
that are supposed to be sent to syslog in these situations.

https://bugs.debian.org/775067