sd-event: change ordering of pending/ratelimited events
    
    Instead of ordering non-pending before pending we should order
    "non-pending OR ratelimited" before "pending AND not-ratelimited".
    This fixes a bug where ratelimited events were ordered at the end of the
    priority queue and could be stuck there for an indeterminate amount of
    time.
    
    (cherry picked from commit 81107b8419c39f726fd2805517a5b9faab204e59)