The text frame is swapped in this case, so handle BTLR similar to the
normal vert (TBRL) case and the background will be positioned correctly
behind the text portion.

Change-Id: I2399131ef74ea8849577a467ad9bb02d980d8609
Reviewed-on: https://gerrit.libreoffice.org/69539
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>