zlisp: return correct value from `goto-char`.

* lib/zemacs/specs/zlisp_move_spec.yaml (goto-char): Specify
return values.
* lib/zile/buffer.lua (goto_offset): Return actual position
moved to.  This is not what Emacs does, but is more useful as a
Zile API this way.
* lib/zemacs/zlisp/move.zl (goto-char): Ignore goto_offset
return value, and simply return the value of the position
parameter as Emacs does.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>