debian: Ensure changelog distribution is tagged

UNRELEASED should not be left as-is when actually releasing.
The latest changelog entry now point at unstable instead.

The simple d/genchangelog.sh now does `dch -r ''` automatically
to ensure this distribution update doesn't get lost along the way
on future invocations.
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

debian/changelog

-libloc (0.9.8-1) UNRELEASED; urgency=medium
+libloc (0.9.8-1) unstable; urgency=medium
 
   [ Michael Tremer ]
   * importer: Do not try to initialise a column that cannot be NULL with

debian/genchangelog.sh

@@ -31,6 +31,8 @@ main () {
     echo "$author_name <$author_email>  $subject"
     DEBFULLNAME="$author_name" DEBEMAIL="$author_email" debchange --upstream --multimaint-merge "$subject"
   done
+
+  debchange --release ''
 }
 
 main "$@" || exit $?