Don't show empty message while sorting

This changes the ui to show the spinner while we are sorting. It only
shows one line of the spinner since there are an unknown number of
messages at this time.

lib/msgstore.go

@@ -14,6 +14,8 @@ type MessageStore struct {
 	Deleted  map[uint32]interface{}
 	DirInfo  models.DirectoryInfo
 	Messages map[uint32]*models.MessageInfo
+	Sorting  bool
+
 	// Ordered list of known UIDs
 	uids []uint32
 
@@ -185,9 +187,7 @@ func (store *MessageStore) Update(msg types.WorkerMessage) {
 	switch msg := msg.(type) {
 	case *types.DirectoryInfo:
 		store.DirInfo = *msg.Info
-		store.worker.PostAction(&types.FetchDirectoryContents{
-			SortCriteria: store.defaultSortCriteria,
-		}, nil)
+		store.Sort(store.defaultSortCriteria, nil)
 		update = true
 	case *types.DirectoryContents:
 		newMap := make(map[uint32]*models.MessageInfo)
@@ -599,10 +599,14 @@ func (store *MessageStore) ModifyLabels(uids []uint32, add, remove []string,
 }
 
 func (store *MessageStore) Sort(criteria []*types.SortCriterion, cb func()) {
+	store.Sorting = true
 	store.worker.PostAction(&types.FetchDirectoryContents{
 		SortCriteria: criteria,
 	}, func(msg types.WorkerMessage) {
-		cb()
+		store.Sorting = false
+		if cb != nil {
+			cb()
+		}
 	})
 }
 

widgets/msglist.go

@@ -63,6 +63,12 @@ func (ml *MessageList) Draw(ctx *ui.Context) {
 		}
 	}
 
+	if store.Sorting {
+		ml.spinner.Start()
+		ml.spinner.Draw(ctx)
+		return
+	}
+
 	var (
 		needsHeaders []uint32
 		row          int = 0