Handle altname in docx's fonttable.xml

We don't actually need to do anything with altname, so just break.

Change-Id: I4b20d762c730675acb79ea1a4f0c5c14e7b86752
Reviewed-on: https://gerrit.libreoffice.org/8616
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>