Error is silently logged when new window is opened

[EtiamNullam]

Error

Error detected while processing function <SNR>55_SetupAutoCommands[30]..<SNR>55_ClearHighlighting:
line    1:
E803: ID not found: 4

Steps to reproduce

0. Install/activate this plugin
1. :redir @a
2. :new (:split also works)
3. "ap

Specs

Windows 10
NVIM v0.5.0 - v0.8.0 (nightly)

[Cimbali]

Interesting. I can reproduce on vim 8.2 with a slightly different message:

Error detected while processing WinEnter Autocommands for "*"..function <SNR>43_SetupAutoCommands[11]..<SNR>43_HighlightEOLWhitespace[1]..<SNR>43_ClearHighlighting:
line    1:
E803: ID not found: 4

[Cimbali]

Actually that is an intentionally silenced message:

vim-better-whitespace/plugin/better-whitespace.vim

Lines 190 to 192 in c5afbe9

	function! s:ClearHighlighting()
	silent! call matchdelete(get(s:, 'match_id', -1))
	endfunction

I did not know that silenced messages appeared in redirected output. If you start vim with vim --cmd "redir @" you’ll see that we also silence an error on opening vim. In any case there’s 2 tiny issues here:

• we use s: for the match ID but these ids are bound to windows, hence in a new window the existing id do not make sense
• matchdelete does not accept -1

[ntpeters]

Reopening per #154