less: escape newlines in file names

less: escape newlines in file names

Newlines in a filename can lead to arbitrary code execution
https://marc.info/?l=oss-security&m=171292433330233&w=2
via LESSOPEN.  The diff is a straightforward adaptation of
https://github.com/gwsw/less/commit/007521ac3c95bc76

The better fix is deleting the misfeatures that are LESSOPEN
and LESSCLOSE which will happen in a separate commit.

diff looks good to guenther