bug#63337: [PATCH] package-vc--build-documentation: Fix relative @include statements

[Eli Zaretskii]

> From: Philip Kaludercic <philipk@posteo.net>
> Cc: Eli Zaretskii <eliz@gnu.org>,  63337@debbugs.gnu.org
> Date: Fri, 12 May 2023 06:51:19 +0000
> 
> One issue I still notice in this case is that if the file doesn't exist,
> the issue is raised by `insert-file-contents' which aborts the entire
> installation.  Does checking the existence of the file, and continuing
> on if this is not the case make sense:

If the file's (non)existence is the problem, then checking that up
front is an okay solution, IMO.  Are there any downsides to doing that?