fix bug in do_justify() in a better way: add on_next_line flag, used to

fix bug in do_justify() in a better way: add on_next_line flag, used to
indicate when we've moved to the next line after justifying the current
line, and only run the respacing routine when it's true; this keeps the
respacing routine from erroneously being run more than once on the same
line

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@1840 35c25a1d-7b9e-4130-9fde-d3aeb78583b8