r24241 (#6755) introduced a bug where if the KDC sends a LastReq entry
containing an account expiry time, we send a prompter warning for
password expiry even if there was no entry containing a password
expiry time.  Typically, this results in the message "Warning: Your
password will expire in less than one hour on Thu Jan  1 12:00:00
1970".

Fix this by explicitly checking for pw_exp == 0 in warn_pw_expiry()
after we've gotten past the conditional for invoking the callback.

https://github.com/krb5/krb5/commit/1624388ff4621b24dd855fbcc61bd19ebf7217fa
Commit By: ghudson
Revision: 25730
Changed Files:
U   trunk/src/lib/krb5/krb/gic_pwd.c