fix: window picker ignore hidden window

[phanen]

Hidden win should never be used as target.

repro

Use neovim nightly

for name, url in pairs {
  nvt = 'https://github.com/nvim-tree/nvim-tree.lua',
} do
  local install_path = vim.fn.fnamemodify('nvim_issue/' .. name, ':p')
  if vim.fn.isdirectory(install_path) == 0 then
    vim.fn.system { 'git', 'clone', '--depth=1', url, install_path }
  end
  vim.opt.runtimepath:append(install_path)
end
require('nvim-tree').setup {}
require('vim._extui').enable({})

nvim --clean -u nvim-tree-hide.lua +"%bd!" +NvimTreeOpen

[alex-courtis]

Many thanks for the quick fix @phanen !