Problem: with `show_hidden = false`, a directory containing only
dotfiles renders as just `..`, giving no indication that entries exist.
Solution: add `view_options.show_hidden_when_empty` (boolean, default
false). After the main filter loop in `render_buffer`, if the option is
set and `#line_table <= 1`, iterate `entry_list` again and render any
entry not matched by `is_always_hidden`, using `is_hidden = true` so
they render with the dimmed hidden style.
Based on: stevearc/oil.nvim#473
Barrett Ruth
2fe4e78807
