Fix crash when items have to be moved around after a labyrinth shift.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@7392 c06c8d41-db1a-0410-9941-cceddc491573

Created by  j-p-e-g  on November 6, 2008
5ONUB5WXLAKG2V4HGFHJQR6WWSBUZQ2DZOWIS73G7AVWWB6PBHXAC
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