BUG #8139: initdb: Misleading error message when current user not in /etc/passwd

The following bug has been logged on the website:

Bug reference: 8139
Logged by: Nicolas Marchildon
Email address: nicolas(at)marchildon(dot)net
PostgreSQL version: 9.2.4
Operating system: RHEL 6
Description:

Running initdb while logged in as a user that has no entry in /etc/passwd,
which happens when authenticating with Kerberos, and missing sssd-client
prints a misleading error message:

"initdb: could not obtain information about current user: Success"

The misleading part is the "Success". This comes from errno:

pw = getpwuid(geteuid());
if (!pw)
{
fprintf(stderr,
_("%s: could not obtain information about current
user: %s\n"),
progname, strerror(errno));
exit(1);
}

The man page says:

RETURN VALUE
The getpwnam() and getpwuid() functions return a pointer to a
passwd
structure, or NULL if the matching entry is not found or an
error
occurs. If an error occurs, errno is set appropriately. If one
wants
to check errno after the call, it should be set to zero before
the
call.

First, initdb's get_id function does not set errno to zero, which is a bug.
Second, when the return value is NULL, it should only print strerror(errno)
when errno != 0.