honor canceled context and do not leak on mergeChannels

mergeEntryChannels has the potential to perpetually
wait on the results channel, context might be closed
and we did not honor the caller context canceling.

cmd/metacache-entries.go

@@ -695,8 +695,12 @@ func mergeEntryChannels(ctx context.Context, in []chan metaCacheEntry, out chan<
 			}
 		}
 		if best.name > last {
-			out <- *best
-			last = best.name
+			select {
+			case <-ctxDone:
+				return ctx.Err()
+			case out <- *best:
+				last = best.name
+			}
 		} else if serverDebugLog {
 			console.Debugln("mergeEntryChannels: discarding duplicate", best.name, "<=", last)
 		}

cmd/metacache-server-pool.go

@@ -554,11 +554,11 @@ func (z *erasureServerPools) listMerged(ctx context.Context, o listPathOptions,
 	for _, pool := range z.serverPools {
 		for _, set := range pool.sets {
 			wg.Add(1)
-			results := make(chan metaCacheEntry, 100)
-			inputs = append(inputs, results)
+			innerResults := make(chan metaCacheEntry, 100)
+			inputs = append(inputs, innerResults)
 			go func(i int, set *erasureObjects) {
 				defer wg.Done()
-				err := set.listPath(listCtx, o, results)
+				err := set.listPath(listCtx, o, innerResults)
 				mu.Lock()
 				defer mu.Unlock()
 				if err == nil {
@@ -609,6 +609,7 @@ func (z *erasureServerPools) listMerged(ctx context.Context, o listPathOptions,
 	if err != nil {
 		return err
 	}
+
 	if contextCanceled(ctx) {
 		return ctx.Err()
 	}