fix: additional handling of potentially non-existent files, just in case

lua/jj-log/init.lua

···
     return
   end
 
+  if not vim.fn.filereadable(current_file) then
+    vim.api.nvim_buf_del_var(bufnr, "jj_desc")
+    return
+  end
+
   local jj_root = vim.fs.find(
     ".jj", {
       upward = true,