in cut_marked_segment(), respect concatenate_cut, as we need to use it

in cut_marked_segment(), respect concatenate_cut, as we need to use it
if we do a marked cut and immediately follow it with a cut-to-end (which
uses that function)

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@2095 35c25a1d-7b9e-4130-9fde-d3aeb78583b8