Small issue in handling of `shadowMax` attribute of `shadowAccount`

[Dark Colour <thedarkcolour [at] gmail.com>]

Hi,

I encountered an issue where nss-pam-ldapd interprets 0 and negative values of shadowMax to mean that an LDAP user's password has expired. On other operating systems that use sssd, nss-ldap, and ypldap, 0 is interpreted as "never expires," but nss-pam-ldapd is hardcoded to only interpret a value of -1 (the default if the attribute is missing) as "never expires."

The fix is changing line 354 in ./nslcd/pam.c from this:
 else if (maxdays != -1)
 {
   /* check maxdays */
   daysleft = lastchangedate + maxdays - today;
   if (daysleft == 0)
     mysnprintf(authzmsg, authzmsgsz - 1, "Password will expire today");
   else if (daysleft < 0)
     mysnprintf(authzmsg, authzmsgsz - 1, "Password expired %ld days ago",
                -daysleft); 

to this:

else if (maxdays > 0)

I've described the issue in more detail on GitHub, but I wasn't sure if that was the best way to reach you:
https://github.com/arthurdejong/nss-pam-ldapd/issues/75

Thank you for working on this project.