Initialization fix for dynamic folders

There is an issue with backends, that provide dynamic folders, namely
when opening folder, that isn't defined in config file, you get empty
folder. To actually get messages listed, you need to open that folder
twice.

At first attempt only DirectoryInfo is fetched and new
MessageStore created. Second attempt populates previously created
MessageStore with list of messages.

For pre-configured folders, DirectoryInfos are fetched upon connection
to backend and, when folder is opened, MessageStore is updated with list
of messages.

Fixes: https://todo.sr.ht/~rjarry/aerc/30
Signed-off-by: Aivars Vaivods <aivars@vaivods.lv>
Acked-by: Robin Jarry <robin@jarry.cc>

widgets/dirlist.go

@@ -133,6 +133,12 @@ func (dirlist *DirectoryList) Select(name string) {
 
 		select {
 		case <-time.After(dirlist.UiConfig().DirListDelay):
+			newStore := true
+			for _, s := range dirlist.store.List() {
+				if s == dirlist.selecting {
+					newStore = false
+				}
+			}
 			dirlist.worker.PostAction(&types.OpenDirectory{Directory: name},
 				func(msg types.WorkerMessage) {
 					switch msg.(type) {
@@ -156,6 +162,9 @@ func (dirlist *DirectoryList) Select(name string) {
 							sort.Strings(dirlist.dirs)
 						}
 						dirlist.sortDirsByFoldersSortConfig()
+						if newStore {
+							dirlist.worker.PostAction(&types.FetchDirectoryContents{}, nil)
+						}
 					}
 					dirlist.Invalidate()
 				})