Small fix for previous check-in to prevent writes outside mini-map array bounds.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@3421 c06c8d41-db1a-0410-9941-cceddc491573

Created by  ennewalker  on February 9, 2008
H5CCPXNHFSQ3SBRGB72XZTFD2U77DP7ZMW2SXXKD7DD3EO732QDQC
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