fix: skip normalizing empty file paths

[bwpge]

This PR fixes a quite niche Windows bug where quickly changing popup windows could cause Neo-tree to try and follow (and thus normalize) an nil file path. This causes an error message to be printed, despite not actually being an issue for Neo-tree.

Essentially the problem is:

• Some form of popup window (like NuiInput) closes, changing the active buffer
• This causes the "follow" event to be fired from Neo-tree, but it is debounced:

  neo-tree.nvim/lua/neo-tree/sources/filesystem/init.lua

  Line 105 in 7d3b020

  utils.debounce("neo-tree-follow", function()

• A toggleterm floating window is opened (triggered from the previous NuiInput by on_submit) and changes the active buffer to be a term:// path before the debounce timer finishes
• The follow_internal function does not include term:// paths when calling manager.get_path_to_reveal() so it returns nil and passes that directly into normalize_path:

  neo-tree.nvim/lua/neo-tree/sources/filesystem/init.lua

  Line 33 in 7d3b020

  local path_to_reveal = utils.normalize_path(manager.get_path_to_reveal())

• On Windows, this path value is indexed here, but the function does not check for nil (note the doc comment states the argument is a string not string?):

  neo-tree.nvim/lua/neo-tree/utils/init.lua

  Line 763 in 7d3b020

  path = path:sub(1, 1):upper() .. path:sub(2)

• Thus an error occurs before the follow_internal can gracefully exit early from an empty path here:

  neo-tree.nvim/lua/neo-tree/sources/filesystem/init.lua

  Line 34 in 7d3b020

  if not utils.truthy(path_to_reveal) then

The check is only added after the M.is_windows branch, so this will not change behavior for any non-Windows users. Windows users will have the exact same behavior (no file will be followed), just without the error message.

See below comment.

[bwpge]

After looking at this again, I realized there was a more correct fix, e.g., not passing nil to a function that only accepts string arguments. This fixes the same problem, but doesn't add an extra branch check to every Windows call to normalize_path.

[cseickel]

Looks good. Thanks for the fix!