Fix #468

In background mode, the thread that flushed the memory DB
couldn't be joined because it started before the filesystem
initialization.

bin/gdfuse.ml

@@ -326,7 +326,6 @@ let setup_application params =
   end else begin
     DbCache.reset_clean_shutdown cache;
   end;
-  MemoryCache.start_flush_db_thread cache;
   let refresh_token = context |. Context.refresh_token_lens in
   if refresh_token = "" then
     if client_id = "" || client_secret = "" then

src/drive.ml

@@ -1032,6 +1032,8 @@ let get_metadata () =
 
 let init_filesystem () =
   let context = Context.get_ctx () in
+  let cache = context.Context.cache in
+  MemoryCache.start_flush_db_thread cache;
   let config = context |. Context.config_lens in
   let root_folder_id = do_request (get_root_folder_id config) |> fst in
   Context.update_ctx (Context.root_folder_id ^= Some root_folder_id)