Ticket 48928 log of page result cookie should log empty cookie with a different value than 0
    
    Bug Description:
        With the ticket https://fedorahosted.org/389/ticket/48752, the cookie value
        is logged with each page result RESULT.
        When the page result is completed (no more entry to return), the returned cookie is 'pr_cookie=0'.
        Else the cookie value is logged 'pr_cookie=<internal index>'. Unfortunately the index ranges [0..N].
    
        So when the value pr_cookie=0 is logged, it is not possible to know if it is an empty cookie or a valid cookie with the value 0.
    
    Fix Description:
        Log the empty cookie with a value '-1'
    
    https://fedorahosted.org/389/ticket/48928
    
    Reviewed by: Noriko Hosoi, Simon Pichugin (thanks !!!!)
    
    Platforms tested: F23
    
    Flag Day: no
    
    Doc impact: no