Ticket 49267 - autosize split of 0 results in dbcache of 0
    
    Bug Description:  autosize split of 0 results in a dbcache of 0. This was
    due to a missing bounds check on the value for 0. In theory this could
    still be problematic if the value was say 1% ... But hopefully we don't
    see that :)
    
    Fix Description:  Add the bounds check.
    
    https://pagure.io/389-ds-base/issue/49267
    
    Author: wibrown
    
    Review by: mreynolds (Thanks!)
    
    (cherry picked from commit 22d4865ea20acb6e6c11aed10d09241b09bb711c)