bug#40808: 27.0.91; inaccuracy in isearch-lazy-count

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Cc: Abdullah Asad <abdullah@net-c.com>,  40808@debbugs.gnu.org
> Date: Wed, 29 Apr 2020 02:54:06 +0300
> 
> But there is still one corner case I'm worried about:
> isearch-lazy-count still counts matches that can't be opened
> and can't be visited, such as hidden links in org-mode.
> 
> To not count them we need to bind 'search-invisible' to 'open'
> in isearch-lazy-highlight-search, but the problem is that
> isearch-filter-predicate and isearch-range-invisible will
> temporarily open them, whereas we need just to check
> whether they can be opened.
> 
> So in the following patch I added a new variable isearch-check-overlays
> that could instruct isearch-range-invisible to not open overlays
> when it's non-nil that means we need only to check them, not open:

Fine with me, but please make this change on master, not on emacs-27.