fix: invalid window id for popup info window

[yavorski]

Hi, this solves an error when the info window is closed via fclose - vim.cmd("fclose"). I have this in a keymap bind to ESC and get this error:

x Error  12:13:38 msg_show.lua_error Error detected while processing CursorMoved Autocommands for "*":
Error executing lua callback: .../nvim-tree.lua/lua/nvim-tree/actions/node/file-popup.lua:60: Invalid window id: 1004
stack traceback:
[C]: in function 'nvim_win_close'
.../nvim-tree.lua/lua/nvim-tree/actions/node/file-popup.lua:60: in function <.../nvim-tree.lua/lua/nvim-tree/actions/node/file-popup.lua:58>

The fix is to check if window id is still valid.

[alex-courtis]

Great find @yavorski !

Works as intended, however the autocommand still remains. You can see this via:
:au NvimTreeRemoveFilePopup

Suggestion: wrap the nvim_win_is_valid check only around the nvim_win_close