vim:autocmd: Check if same cword when highlighting

When highlighting the current word, check if it is the same as the
currently highlighted one, so that matchdelete and matchadd are not
called unnecessarily.

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

@@ -53,11 +53,16 @@ augroup END
 
 " Highlight word under cursor
 function! HighlightCurrentWord()
+	if exists('w:old_cword') && w:old_cword == expand('<cword>')
+		" Do not delete and readd the match if on the same word
+		return
+	endif
 	if exists('w:cword_match_id')
 		call matchdelete(w:cword_match_id)
 		unlet w:cword_match_id
 	endif
 	if (expand('<cword>') != '')
+		let w:old_cword = expand('<cword>')
 		let w:cword_match_id = matchadd(
 			\ 'CursorColumn',
 			\ '\V\<' . escape(expand('<cword>'), '/\') . '\>',