Restore session with empty file, display Dashboard

[Abao]

Describe the bug
When restore a session with empty file opened, will display Dashboard, and display a error

Error executing vim.schedule lua callback: /usr/share/nvim/runtime/lua/vim/treesitter/language.lua:104: no parser for 'dashboard' language, see :help treesitter-parsers

To Reproduce
Steps to reproduce the behavior:

1. touch empty filetouch test.norg
2. open nvim vim
3. open empty file :e test.norg, but don't input anything
4. save session :mksession test.session
5. quit nvim :q
6. restore sesion vim -S test.session

Expected behavior
don't show dashboard and show opened empty file correctly

Related code

plugin/dashboard.lua