Patch from bug #55650 from Andrej - Avoid AIOOBE if a non-existant Xfs is requested for a styleAvoid AIOOBE if a non-existant Xfs is requested for a style

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1534818 13f79535-47bb-0310-9956-ffa450edef68