Properly handle Xom's failing to summon hostile monsters.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@6121 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on June 24, 2008
CQE2PS6RJI7QIP5YWGJKM6227HSIP7ZB2CBCJH5S2FN3PUDMLXUQC
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