Reinstate a call to DontExpandFormat which was removed from
appendTextContent in commit 232ad2f2

This ensures that direct character formatting which ended immediately
before the insertion point will not be expanded to cover the inserted
content.

Change-Id: Ie5fa6b5c5acee4f885f9e67535e98801af23661a
Reviewed-on: https://gerrit.libreoffice.org/50729Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>