When setting foldlevel to 0 and load some plugin via InsertEnter event
using packer.nvim, if we press i to go to insert mode, the fold for vim
script file will be automatically closed. It is really annoying.
I have pinpoint the issue to the combination of packer.nvim and setting
foldlevel to 0 in after/ftplugin/vim.vim. What is interesting is that
default value for foldlevel is also 0. However, if we do not set it in
vim.vim, the above issue won't occur, which is strange.