SYSDB: Fix uninitialized scalar variable
    
    The boolean variable newly_created could be used uninitialized
    in done section in case of failure. The variable was firstly initialized
    to true after succesfull execution of function sysdb_cache_create_empty.
    
    Uninitialized variable usually means true for boolean variable.
    
    Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>