CPack-deb: don't add a line with a dot to pkg desc
Currently, if the package description ends with a newline
(typically if it is read from a file) cpack -deb adds a single line
with a dot at the end which leads to a violation of the
extended-description-contains-empty-paragraph
debian policy.
This commit fixes the above behaviour.
Fixes: #20763 (closed)
Backport: release
Edited by Kyle Edwards