Prevented divide-by-zero error in rectangle_dimensions().
Shrunk clamping rectangle in clamp_in_bounds() one square away from each side to prevent floor squares from ever abutting the very edge of the level grid.
git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@7652 c06c8d41-db1a-0410-9941-cceddc491573
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