perf(storage): minor optimization for FetchJobs

- Replace a call to fmt.Sprintf with a concatenation
- Explicit declaration of return values in FetchJobs
- Initialize the size of FetchJobs return value to b.limit: when b.limit is
  used, which is most of the time, this avoid resizing the slice, and when it
  isn't, the size of the map is set to 0, which is equivalent to the previous
  situation anyway.
- Move a call to `request.UserID(r)` to a lower scope.

internal/ui/feed_refresh.go

@@ -33,7 +33,6 @@ func (h *handler) refreshFeed(w http.ResponseWriter, r *http.Request) {
 }
 
 func (h *handler) refreshAllFeeds(w http.ResponseWriter, r *http.Request) {
-	userID := request.UserID(r)
 	printer := locale.NewPrinter(request.UserLanguage(r))
 	sess := session.New(h.store, request.SessionID(r))
 
@@ -42,6 +41,7 @@ func (h *handler) refreshAllFeeds(w http.ResponseWriter, r *http.Request) {
 		time := config.Opts.ForceRefreshInterval()
 		sess.NewFlashErrorMessage(printer.Plural("alert.too_many_feeds_refresh", time, time))
 	} else {
+		userID := request.UserID(r)
 		// We allow the end-user to force refresh all its feeds
 		// without taking into consideration the number of errors.
 		batchBuilder := h.store.NewBatchBuilder()