fix paragraph searching code regression: if trying to move to the line

fix paragraph searching code regression: if trying to move to the line
after the end of the next paragraph leaves us on the same line where we
were before, the search should fail in order to avoid an infinite loop

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@2383 35c25a1d-7b9e-4130-9fde-d3aeb78583b8