fdo#67238: sw: fix table cell Unprotect

SwDoc::UnProtectCells() was setting the old box format (from aFmts)
instead of the new one, and actually these 2 vectors are a map.

(regression from 772101649cf16233bbaf0900aa9ebbc915151a95)

Change-Id: I0881a1c499c51b5f3c257e9def1a2e9a00bcb639
(cherry picked from commit b2f9d1b43e4b14cc48327cdce14a03c826096579)
Reviewed-on: https://gerrit.libreoffice.org/7638
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>