[2471488] Fixing crash from randart books. (We probably need randart book tiles anyway...)

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@8173 c06c8d41-db1a-0410-9941-cceddc491573

Created by  ennewalker  on January 3, 2009
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