remember column style during XLSX import, fdo#70315

WE overwrote the column style that was set earlier with the default
style.

Change-Id: I4c02e1cdd3e72f27d75b8153e2af45b5658ff456
(cherry picked from commit 512a14438c4098ca2e30d0b10b6e18506c8475f1)
Reviewed-on: https://gerrit.libreoffice.org/6528
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>