Ticket #47391 - deleting and adding userpassword fails to update the password
    
    Bug description: Deleting and adding password operation causes
    the crash since once an entry is written to and retrieved from
    DB, it does not have unhashed#user#password in the entry any
    more. The delete userpassword internally invokes delete unhashed
    existed in the entry.
    
    Fix description: This patch adds the stricter check for the NULL
    reference.
    
    https://fedorahosted.org/389/ticket/47391
    
    Reviewed by Nathan (Thanks!!)