Do not call sss_cmd_done in function check_cache.
    
    Function sysdb_getpwnam return more results than 1 and therefore sss_cmd_done
    was called. Inside of function sss_cmd_done memory was freed,
    but this freed memory was used in caller functions, therefore sssd crashed.
    
    https://fedorahosted.org/sssd/ticket/1980