optimize a bit

weed/filer/filerstore_wrapper.go

@@ -285,8 +285,10 @@ func (fsw *FilerStoreWrapper) prefixFilterEntries(ctx context.Context, dirPath u
 
 	count := int64(0)
 	for count < limit && len(notPrefixed) > 0 {
+		var isLastItemHasPrefix bool
 		for _, entry := range notPrefixed {
 			if strings.HasPrefix(entry.Name(), prefix) {
+				isLastItemHasPrefix = true
 				count++
 				if !eachEntryFunc(entry) {
 					return
@@ -294,9 +296,11 @@ func (fsw *FilerStoreWrapper) prefixFilterEntries(ctx context.Context, dirPath u
 				if count >= limit {
 					break
 				}
+			} else {
+				isLastItemHasPrefix = false
 			}
 		}
-		if count < limit {
+		if count < limit && isLastItemHasPrefix {
 			notPrefixed = notPrefixed[:0]
 			lastFileName, err = actualStore.ListDirectoryEntries(ctx, dirPath, lastFileName, false, limit, func(entry *Entry) bool {
 				notPrefixed = append(notPrefixed, entry)