ipa-kdb: avoid ENOMEM when all SIDs are filtered out
    
    When all SIDs in info3.sids structure were filtered out, we tried
    to talloc_realloc to zero memory size. talloc_realloc then returned
    NULL pointer and filter_login_info returned with ENOMEM.
    
    The code now rather frees the SID array and set info3.sidcount to
    correct value.