vim:autocommands: Reset old_cword when deleting

When deleting the match, w:old_cword has to be unset as well. Otherwise
it can happen that it is not properly readded (e.g. when moving from a
word to an empty line and then back to the same word).

.config/vim/vimrc.d/80-autocommands.vim

@@ -60,6 +60,7 @@ function! HighlightCurrentWord()
 	if exists('w:cword_match_id')
 		call matchdelete(w:cword_match_id)
 		unlet w:cword_match_id
+		unlet w:old_cword
 	endif
 	if (expand('<cword>') != '')
 		let w:old_cword = expand('<cword>')