MM-18623 - invalid reply-count displayed (#12364)

* fixed thread creator, fixed default behaviour of fetching posts
* handle reply-count in getPostThread code path

app/plugin_api.go

@@ -466,7 +466,7 @@ func (api *PluginAPI) DeletePost(postId string) *model.AppError {
 }
 
 func (api *PluginAPI) GetPostThread(postId string) (*model.PostList, *model.AppError) {
-	return api.app.GetPostThread(postId)
+	return api.app.GetPostThread(postId, false)
 }
 
 func (api *PluginAPI) GetPost(postId string) (*model.Post, *model.AppError) {