Wrong queue waiting possition when canceled in the middle of the waiting list

[wtsergo]

Hello,

I believe there is a bug in queue position resolution for the waiting consumers when cancellation happens in the middle of the waiting list.
Attaching script to reproduce the bug.
queue_waiting_position.txt
Expected output is
IT1: 0 => 0 IT3: 1 => 1 IT1: 2 => 2 IT3: 3 => 3
Actual output
IT1: -1 => 0 IT3: 1 => 1 IT1: 2 => 2 IT3: 3 => 3

Also attaching proposed fix
fix-waiting-position.diff.txt

Thanks,
Sergey