getFontFamily() can give a different result on the second call so in
order to protect against access to an invalid element of the vector
the result must be reused.

Change-Id: Iec7d58537263cb5c8a7c2ea95761dd929d659e01
Reviewed-on: https://gerrit.libreoffice.org/25704Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Xisco Faulí <anistenis@gmail.com>