[#1047] policer: Check context before job selection

When application is being terminated, replicator routine
might be on the object picking phase. Storage is terminated
asynchronously, thus `Select()` may return corresponding
error. If we don't process `context.Done()` in this case,
then application freezes on shutdown.

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pkg/services/policer/process.go

@@ -27,6 +27,12 @@ func (p *Policer) shardPolicyWorker(ctx context.Context) {
 	)
 
 	for {
+		select {
+		case <-ctx.Done():
+			return
+		default:
+		}
+
 		addrs, cursor, err = p.jobQueue.Select(cursor, p.batchSize)
 		if err != nil {
 			if errors.Is(err, engine.ErrEndOfListing) {