Doesn't honor search-invisible

[QiangF]

The desired behaviour is when search-invisible is set to nil, don't search inside the invisible area. There are cases that the user don't want to search in the hidden area. One example is dired-mode with git-annex font lock enabled, file symlinks targets are hidden sha256 strings, it makes no sease to search those hidden symlinks. Another use case is org mode with partly folded headings.

[raxod502]

Thanks for pointing out this problem. I don't have time right now to implement a solution, but I would be able to review and merge a pull request adding logic to handle the case. It should be rather similar to https://github.com/raxod502/ctrlf/issues/23, porting logic over from Isearch for compatibility.