this patch fixes several issues:

- any cell containing a formula above row 1024 causing a tile
invalidation whenever any cell content was changed, even if unrelated
to the formula;

- any formula below row 1024 wasn't updated even if it was inside the
visible area.

Change-Id: Ib92153d5755c4e231aa68dee807fe997f9e80a46
Reviewed-on: https://gerrit.libreoffice.org/53932Reviewed-by: Jan Holesovsky <kendy@collabora.com>
Tested-by: Jan Holesovsky <kendy@collabora.com>