up to maximal size of primFontSz constraint.
Do not override text size changed by user.

Change-Id: If7ea6bbb96cb839831d877edc274a1b0eefdaf21
Reviewed-on: https://gerrit.libreoffice.org/73050
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>