fix: disable autostart after :LspStop #2987

Problem:
The `BufReadPost` handler may autostart LSP, even after `:LspStop`.

Solution:
Remove the `BufReadPost` handler if there are no clients (assuming that
`:LspStop` stopped them).

Note: The `BufReadPost` handler will be recreated if user runs `:LspStart`.

lua/lspconfig/configs.lua

@@ -139,6 +139,9 @@ function configs.__newindex(t, config_name, config_def)
           api.nvim_create_autocmd('BufReadPost', {
             pattern = fn.fnameescape(root_dir) .. '/*',
             callback = function(arg)
+              if #M.manager:clients() == 0 then
+                return true
+              end
               M.manager:try_add_wrapper(arg.buf, root_dir)
             end,
             group = lsp_group,