RegisterPeriodicChain() returns nil if lock cannot be accquired

[charleswhchan]

Is there a bug in the following code:

		err := server.lock.LockWithRetries(utils.GetLockName(name, spec), schedule.Next(time.Now()).UnixNano()-1)
		if err != nil {
			return        # returns nil; expect err
		}

See:

• machinery/v1/server.go

  Line 397 in ef4a2e7

  return

• machinery/v2/server.go

  Line 337 in ef4a2e7

  return