fix: #33

[epheien]

plugin/* will not loaded when it modify rtp in autocmd, such as:

autocmd FileType * ++once set rtp+=~/myconf/vim/pckr/opt/nvim-lspconfig

so pckr need to load them

I try to use not vim.tbl_isempty(vim.v.event) check if in autocmd context, but it failed, seems it is a bug of nvim