Summoned monsters' disappearing wasn't being taken into account after handling monster enchantments; a disappeared monster would have a type of -1; and the call to mons_habitat(), which looked at the monster type, would crash.
git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@3210 c06c8d41-db1a-0410-9941-cceddc491573
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