variable for a little optimization.

Openfile can never be NULL -- it should have been called openbuffer, and
before we start fiddling with the cursor, we will always have an open buffer.
Edittop might be NULL, but that's okay.


git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@5763 35c25a1d-7b9e-4130-9fde-d3aeb78583b8