Fix enqueue jobs

[seitau]

Fixed: #260

Fixed issue with rescheduling jobs. The cause of the problem was the use of pointer when sending jobs to channel.
The previous implementation was sending pointer of j to channel and it resulted in that queued jobs reference same address.

So I fixed to send each job's pointer to channel.

Before

for _, j := range jobs {
  wp.tryEnqueue(&j, true)
}

After

for i := range jobs {
  wp.tryEnqueue(&jobs[i], true)
}

[nanuuki]

Nice catch @seita-uc and thank you for the fix! 👍