fdo#75260: Apply the same fix from writer table to character bordering.

And mirror the right and bottom borders while I'm at it. I guess it was
originally meant to.

Change-Id: I408b077c1524d19bbadd6f0b284ce204064eb735
(cherry picked from commit 2cd1673f41cb5bd8502a9a48a5721244660fe3a0)
Reviewed-on: https://gerrit.libreoffice.org/8650
Reviewed-by: Fridrich Strba <fridrich@documentfoundation.org>
Tested-by: Fridrich Strba <fridrich@documentfoundation.org>