fix: Preventing removal of necessary root separator on Windows

[Aeceon]

This fixes #985

When a root path was supplied as an argument to the Neotree command or to execute on Windows, the necessary separator was removed. ":Neotree C:", for instance, would become "C:" and this resulted in an empty listing.

Instead of testing if the length of args.dir is greater than 1, this now compares it to 3 on Windows while remaining 1 on other operating systems, including WSL.

   -- Root paths on Windows have 3 characters ("C:\")
    local root_len = vim.fn.has("win32") == 1 and 3 or 1
    if #args.dir > root_len and args.dir:sub(-1) == utils.path_separator then
      args.dir = args.dir:sub(1, -2)
    end

I added a comment as well just to clarify what was going on. Though, maybe it'd be better to have a constant. In utils, there's an is_windows variable set (which includes WSL). Maybe a root_len should be set here as well? I'm going to leave it at this for now, though.

[miversen33]

This works on my windows machine. It took me a bit to wrap my head around why it worked lol but ya it works :) @cseickel this should be good to merge.

[cseickel]

This works on my windows machine. It took me a bit to wrap my head around why it worked lol but ya it works :) @cseickel this should be good to merge.

Thanks for checking @miversen33!