Hi,

In the text below, move point to the second half of the URL and 
execute M-x browse-url-at-point.

```
[![Emacs](https://www.gnu.org/software/emacs/images/emacs.png)](https://www.gnu.org/software/emacs/download.html)
```

Firefox and Chromium-based browsers appear to open the URL "https//www.gnu.org/software/emacs/download.html".
It seems that the ":" following https is deleted, but the browser actually normalizes 
the URL with the duplicate scheme "http://https://".

You can check this by executing M-: (browse-url-url-at-point).

Because thing-at-point-bounds-of-url-at-point function cannot correctly recognize 
URL bounds in the text.

I considered changing the thing-at-point-bounds-of-url-at-point algorithm, but it would be a pain to change it without negatively impacting the current behavior.
Ideally, thing-at-point-bounds-of-url-at-point will be fixed eventually, but for now, the attached patch should easily fix the problem.