holds the zombie base type, so properly use mons_zombie_base() instead.
git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@9342 c06c8d41-db1a-0410-9941-cceddc491573
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speed = base_speed(number) - 2;
speed = base_speed(mons_zombie_base(this)) - 2;